Show up early in the morning! I just went to Disneyland, and found that showing up right when the park opens is the best way to go. I got to hop from one ride to another for about two hours, with practically no waiting at all.
When you buy your ticket, you can also get a "Magic Morning" ticket -- which lets you enter the park an hour earlier on certain days. That was amazing.
So the rules that I figured out were: Get to the park by 8am, leave the park by 6pm, and don't eat dinner in the park.