Brace yourselves... another one of my lenghty, detailed (but hopefully 'worth it') posts.

It’s the method you come up with yourself that's going to work best for you. I was a little confused at first as well but I just tried to figure out what would be the simplest way.
[The above comment was in a thread on just writing scripts [here:
http://forum.rifftrax.com/index.php/topic,14903.0.html], but this stickied thread gets more traffic and will likely be seen a lot more, plus I'm not just commenting on scripting, so I'll respond here, since a fair amount of what was covered there - and more - is covered in this thread. I read all of both before I started my first iRiff. Thanks to all who contributed ideas to each, or I would've been totally lost when I started.]
I agree with mr.b. in the above quote: whatever works for you. But all the ideas given are great springboards to get you started in figuring out what out of this smorgasbord will work for you, as you may try a little of each to figure out what fits with your style. [Though written as plain prose, I numbered the following so that it would be clearer that each paragraph was a mostly-independent step.]
1. I've started my first iRiff. Prior to starting, I'd just commented that I was thinking about the particular riff in a thread (the Halloween Movie LoC). Since I got spontaneous responses that at least two people would be interested (out of the few that were following that thread), I figured the appeal might be pretty high overall. If you want people to actually buy your iRiff - as opposed to your just wanting to riff the film - then you really need to consider if the film had enough appeal for people to give it a try. There are a couple iRiffs for obscure films that aren't VODs in the iRiff listings. One of them was for a discontinued French import with a link to the France branch of Amazon.Com, where the page said, "item not found". With DVDs simply not available, the iRiffs will never get bought.
2. So far, what's worked for me to come up with the script was this: The first thing I did was get familiar with the movie (in the case of what I'm riffing, Karloff's
Frankenstein, that wasn't a problem: it's a favorite film). For a film you've seen only once or twice it would likely be a lot harder to figure out what is actually riffable in it, unless you are going with just superficial comments or events. In other words, the deeper riffs that might be the most enjoyable might be missed if you're barely familiar with the film.
3. Another major thing to do is, if the movie you chose seems very confusing, spend time figuring out what is going on, and what the writer/director wanted viewers to
perceive was going on. If there seems to be logical conflicts within the film (there often are

), then spend a little time trying to figure out what was
supposed to be happening. There is little that is more annoying while watching a riffing than to have the riffer make comments about how "confusing" the film is if a couple minutes thought by the viewer could reconcile the confusion. This is particularly annoying if the riffer talked/riffed over the top of the explanation for what is going on (on rare occasion, Mike, Kevin and Bill have even done this *cough*
DragonWars:D-War*cough*). Basically, if you can't manage to understand the film to the degree that viewers were 'supposed' to, then your riffing of it will suffer for that, because simply drawing attention to a logical conflict is far less amusing than is taking the 'understood' conflict and making a funny comment playing off of that. The latter is funnier to those who are better educated (and 'better educated' seems to be the case of most of those who enjoy the humor in this type of commentary).
4. After watching your film a couple/three times, you can write down some ideas. Personally, I let it 'percolate' for a few days with the movie fresh. During those few days, a bunch of ideas came to me, that I hand wrote into a notebook (handier than running to the computer if I was elsewhere at the time). Later, since those eight pages of thoughts were massively out-of-sequence, I cut the pages up and reordered them to fit the proper sequence for the film and transcribed that into a script form. (Obviously that resequencing is easier with a film you are familiar with: if you don't know roughly where in the film an event happens, it is a logistical nightmare to get it in a typed script form. If you are pretty close, its easy enough to move a comment here and there.)
5. Then I did what someone previously suggested: recording a 'raw' riffing while playing the film. That gets the spontaneous ideas down somewhere, while not interrupting your being comedically 'on' by stopping to write/type what you came up with. [According to the two behind the scenes shows, with MST3K that was solved more easily by having one of the 8 or 9 of them at the computer, typing everything as it was said, while the rest could simply riff spontaneously without having to think about keeping track of what was said. If you don't have a personal stenographer handy, you may want to go with the recording.

]
6. Then, having both some core comments from the hand-written stuff (which - for me - seem to be the 'deepest' riffings, as they were the most thoughtful), and the raw audio riffing (which add 'immediacy'), I sat down at the computer with the script format open, and started to sort-of transcribe what was on the tape. I say, 'sort-of' transcribe, because while some basic ideas from the raw riffing were good, they needed a lot of 'optimizing' to be as funny as possible. During the time I was working on the script, I of course added timecodes to the script entries from what I'd transcribed from the notebook, as well as for the new additions.
7. And, of course, between your pre-prepared riffs from notes and audio recording, there will be occasionally long
dead spaces in your script [I found the presence of a lot of dead spaces especially true in
Frankenstein 
]. There are other comments here and in the "How do you write a script for an iRiff?" thread that cover this. What I found was that many of those ideas work: both watching short segments (10-20 seconds) and see what comes up based on dialogue, or else searching out the background for something to riff. Often the most obscure thing may be the most poignant to some listeners: as Kevin said in one of the MST3K behind the scenes shows, that is the kind of comment where some viewer would be saying, "
get out of my head!". In one of those shows one of them (I think Trace) also said about obscure comments, "We never ask, 'who will get that?' we say, 'the right person will get that.' And don't forget the music: sometimes the music itself can be riffed (it may be inappropriate to the scene, or else deliberately being evocative of another film, for instance).
Oh, another thing: One thing I recently experienced with an iRiff was
too many riffs. When there isn't time enough between riffs to 'get a break', (
or hear any dialogue!) each and every one of them gets less funny. Try for a gap of up to 8-10 seconds between the end of one comment and the start of the next (but don't interrupt too much if there's dense dialogue going on:
the viewer must be able to follow the film). The only way that you can figure out comment spacing is to time saying your lines with the movie, in the tone and at the pace you think would have best effect. Besides the lessening of the amusement factor from riffs being too frequent, it is also next to impossible for a viewer to keep track of what is going on in the film if the riffing is nearly constant and covering up much of the dialougue. They get pulled out of the film by the over-riffing, and then they aren't invested enough in the film to care about the comments. But the biggest problem is if you are riffing from something appearing on-screen (instead of a bit of dialogue), there isn't enough time for anyone to 'search out' what you were riffing in the picture before they are expected to be comprehending the next riff.
I am not yet half-way finished with the script I'm writing, but what I've got - I think - is pretty good. Since I'm where I'm at with it, obviously I can't add anything as far as recording goes. With one exception: make sure that whatever microphone/audio card you use together are fully compatible and don't generate noise before you record a final iRiff MP3 [from the 'raw riffing' I found that my laptop's audio card added a massive amount of noise to the recording throughout, so from that I know that I will have to use my tower to record the final iRiff]. A quiet recording area is also essential; do something like hang a comforter around the area you are working if at all possible to muffle room noises.
Oh, something I just heard in an iRiff that led me to think of something else with recording: if you
have to add in additional lines later (which, let's face it, is highly likely, as only the pros can go straight through and be nearly perfect), is to make sure you have the same acoustics (i.e. the same room, the same sound-muffling [comforter, whatever], same microphone set up at the same distance from you, etc.). It is
extremely distracting if most of the riffs sound like they were recorded in your bathroom, and one or two sound like they were recorded in a busy bus terminal. Obviously the recording situation can't be replicated exactly, but try to keep the sound as consistent as you possibly can.
Just a little tip on promotion. You never know when you can influence a little word of mouth movement. Just today I was browsing through dvds at an Utlimate Electronics store when I heard a girl telling her boyfriend "yes, really. I'm looking for bad movies so we can make fun of them." You'll rarely hear a better person to mention that you're a riffer to. Not sure if they'll buy anything, but they did ask how they could find my stuff as they left. Just keep your ears open in the right situations and don't be afraid to approach people if you really think they'll be open to it.
A great idea! And I'll add to it: if you have even a little bit of graphics abilities (which you probably do, as you have to/had to make a 'movie poster' for your iRiff), use your computer and pre-perforated business card forms that you can buy at any office supply store to make your own iRiff business cards with links to RiffTrax and your iRiffs (as well as, obviously, your iRiffing name).

How cool would it be to - if you get an opening like RoninFox - to walk up, business card in hand and say, "Bond... James Bond..." oops, other situation... walk up, talk a little bit about riffing, and say, "if you are interested in movies with funny commentaries you may find some of these interesting," while handing them a professional-looking card, impressing the hell out of them (possibly enough for them to actually go to the web site).
If you have/give out your business card freely (rather than waiting/hoping that the person will ask for more information), then your name/iRiffs will get more recognition. That's because many people won't ask you for more information on their own. Obviously that's why there's workers asked to say, "may I help you with something?" in stores: people are far less likely to ask than to take you up on an offer if it is given with no effort on their part.
OK... back to your regularly scheduled thread....