Dasher and TDD are spot on, my procedure is this, all 5 shot groups. I research and go with the powder that most seem to be using with success and start with my targeted load, say it's a 300WSM, I know they like H4350 and with a 200 or 210 grain bullet it likes something close to 61 grains. I'll load 5 sets of 5, 60.4, 60.7, 61, 61.3, and 61.6, seated .010" into the lands, head to the range see whats the most accurate, for instance say is was 60.7. I'll then take 5 sets of that powder charge and play with seat depth, -.050", -.025", -.010", 0, and +.010 or some variation of that, find what works best. Then take that seat depth and go with the most accurate powder charge I had and load 3 sets of 5 at .3 plus and minus the most accurate load, in this instance the most accurate was 60.7 so do 60.4, 60.7 and 61.0. You'll quickly determine whats best.
If you don't know or cant find out what powder is the best for your application pick a bullet and seating depth combo and start burning powder, after all that is the fun part
There is a world of wealth when it comes to information, just ask for good combos and more than likely you'll get good answers, keep in mind though, there are some internet hero's that know it all and spend minimal time behind the trigger and the reloading bench. It will take some common sense on your part