Tips for demomakers
How to make good demos (by Phoenix / Hornet & DemoDVD-crew)

Demos are watched in essentially two types of locations: On large screens at demo parties, and afterwards, at the homes of the partygoers after they download them. A truly good demo is enjoyable in both locales.

HOW TO MAKE A DEMO PEOPLE WILL ENJOY AT A PARTY

Keep a limit on the playing time. Most demos have a single song and are under six to seven minutes long. Ten minutes is a good limit for more than one song. Any longer, and you risk losing the interest of the viewers. Much like pop music, the "sweet spot" for demo length is usually four to five minutes. Likewise, each part/scene of the demo shouldn't last more than 30-45 seconds or so.

Maintain a good pace throughout the demo. Like a good movie, a demo should start out light, build up to a heavy climax, and fade back to the end. Save your best effects for the middle of the demo. It doesn't hurt to have one or two slow parts after a fast part, if you want to build up more than once. The pace of the music should follow the pace of the effects. Fast motion warrants fast music, and slow music goes best with slow motion. You can certainly mix fast and slow parts in your music, but you should be able to enjoy listening to it by itself, even without a demo to accompany it.

Make your demo projector-friendly. While you make your demo on a monitor, there are a few pointers you can keep in mind when it's shown on a projector. First, keep video mode changes to a minimum. Projectors typically blank for a couple seconds while changing video modes. Second, give your scenes plenty of brightness and contrast. It's harder to see dark scenes on a projector than on a monitor. Third, know what resolutions the projector will support. Most projectors these days support up to 1024x768, but if they don't, and that's the only video mode your demo supports, you are out of luck.

The "rule of threes" that applies to film applies to demos too! For each part, mentally divide the screen into three equal vertical sections. Is there something interesting in each section? If not, the viewer's attention might wander or vanish. You want their attention on the full screen, all the time.

Effects still impress, but design is king. Code alone won't win a compo anymore. Color schemes, fonts, transitions, and synchronization are all crucial to a winning demo. It never hurts to have someone in your group, other than the main coder, focused on design.

Be dramatic. A good party demo should inspire some kind of emotion in its viewers.

HOW TO MAKE A DEMO PEOPLE WILL ENJOY AT HOME

Don't release a demo unfinished. There's nothing a demo watcher hates more than a demo that builds up after two minutes, then ends abruptly. A demo can be too long, but it can be too short as well.

Test your demos on several computers! This is especially important with modern PC hardware. You may have a demo run great on a GeForce card only to find out it won't run on a Radeon. You'll lose a lot of viewers if that's the case.

Originality is good, repetition is not. Unique effects are the most memorable. Don't keep jumping back to parts you already showed, unless you have plenty of design elements and synchronization to go with them.

Gimmicks can win parties, but quality is remembered. It's easy to throw pop-culture references in your demo to attract party voters, but when they get home they want something that won't get old too quickly.