Leave enough padding in your clips to accommodate transitions. A transition such as Cross Dissolve overlaps portions of two clips and displays them both simultaneously. But if the action begins immediately in the second clip, it will be partially obscured by the dissolving portion of the first clip. Leaving a few seconds of neutral footage gives you the transition effect you want without disrupting the content of the scene. If you end up with too much padding, you can always trim it out when you're fine-tuning your movie.
Speaking of transitions, don't get overly excited about all the different transitions that are available. In most situations, you'll probably use Cross Dissolve, Fade In, Fade Out, and Overlap. Although others can be appropriate at times, using too many flashy transitions tends to distract from the movie itself. It's the same principle as using too many fonts in a word processing document: With more than a few on the page, it no longer matters what the words say.
Sizing Up Titles
In terms of ease of use, the slider that determines a title's font size is wonderfully simple: Slide left to reduce the size, slide right to increase it. However, it can be maddeningly frustrating if you want precision. For one thing, the longer your title, the smaller the text will appear, even at the largest font size. And iMovie's rough title preview can be deceptive about text size and the way in which longer phrases are wrapped to the next line. So, apply your titles to a few dummy clips that you can export back to tape and preview on a television to see exactly how the title will appear.
Using Music Tracks
iMovie has what must have once been an ingenious method of adding music to your movie: You can record song tracks from a CD directly into the program. You can either drag a track from the CD into iMovie's timeline, or start playing the song and record it as it plays, much the way you import video from your camcorder's videotape. However, with MP3 music files and iTunes, this technique has become archaic.
In iMovie, you must start playing the song and record it, the way you import video from your camcorder's videotape. A better solution is to first use iTunes to extract music as MP3 files, and then use iMovie's Import command to add the song to your movie. If you want the highest quality audio (which takes up significantly more disk space), use iTunes to extract the song in AIFF format; that's how iMovie's built-in audio recorder stores music. However, I prefer iTunes's interface and its capability to assign track names from the CDDB database of song titles (instead of iMovie's generic "Track 02" naming scheme).
This article originally appeared in slightly different form on the TidBITS Web site, where Jeff Carlson is Managing Editor.