I like doing multiple sets at your lightest warm-up weight to really get warm before you start moving up. This takes more time, but I find people feel much better, and this doesn't really tire you out at all. For example, I'll snatch 50 3-4 sets of 2 before I start moving up.
After that, the idea is to get warm and prepared with as little fatigue as possible. Something like 6-8 sets to get to your opener is usually about right. Take bigger jumps early and smaller jumps as you reach your last warm-up weight.
But also as Blake said, you need to be confident during your warm-up and especially for your opening lift, so don't change anything drastically from what you would do normally when working up to a heavy single or max attempt.