Our club has not built our own float, but has instead made the class floats move. Here's what we have to say:

1. Only work on the structure, let them decorate it. They like it a lot better this way, and it helps to have two teams to tackle different tasks: one to make it move, one to decorate.
2. Wood, Wood, Wood. You'll need more wood than you think at first. This year I'm in charge of making a giant moving spongebob, and I can tell it's going to be quite a large project. Also, wood is fast and easy to work with, and it doesn't have to be nearly as precise as metal
3. Make sure your breakers are correct. We had an issue with this, as a drivetrain guy did the wiring. Flaming control panels are not fun mid parade.
4. Isolate the battery/electronics. This is a general safety tip, as in case of emergency, it's better to not risk all that flameable tissue paper. Besides, though colored flames look pretty, the fire department has this issue with large moving bonfires.
5. Limit the complexity of moving objects. If it's more than three stages of chain just to make one thing spin, it's too complex. We had an issue with this, and it was annoying to tune/get running.
6. Don't let just anyone run the float without the team in charge of it present. This resulted in our beautifully designed float being in a non working state for the actual parade. And if something is supposed to be moving, and isn't, it just doesn't look that cool.
7. Make all the designs very robust and simple. It needs to be reliable, as it will be running more than you think.
8. Make it (the moving mechanism) easy to access. Due to Murphy's law, something will break 5 minutes before the parade starts. Therefore it makes sense to be able to quickly access everything for quick fixes.

Hope that helps, and if you have any more questions, just pm or email me!