typically 3/4 of a cup of priming sugar is good for 5 gallons. Mix it with about 2 cups of water and boil it. Cool it down a bit and add to your bottling bucket, then rack the beer onto it. That will usually distribute the priming sugar evenly throughout the beer but if you want to be extra sure, stir gently with a sanitized spoon
Tasty Brew has a nice online calculator. Different types of beer call for different levels of suds, so while that's commonly in the 3/4 cup, or 4-5 oz range for dextrose, it can be different, and it can make a big difference in the way your beer tastes if it's not carbonated to suit the brew.
When adding priming sugar/racking i like to angle my hose to run sideways along the side/bottom of the bucket to make it all move in a swirling motion. +1 on the 3/4 cup with two cups of water. I usually don't even cool it, i start my siphon and wait till there is about 1/2" or so at the bottom of my bottling bucket then pour the dissolved priming sugar in.