You will need to purchase a little bit of everything in the bullet weight you are planing on shooting according to the twist rate of your barrel, Know two same guns are going to shoot the same brand of ammo, so you will need to figure out what your gun likes best, make sure you clean between differant brands, don't mess with the sights as you are looking for good groups not bulls eyes, and shoot with a cold bore (allow 3-4 minutes between shots) once you find what is grouping best for your gun, now you can start fine tuning and getting your persision bulls eye shots, some guns will shoot multiple brands with very good results, the main thing is to get the one that shoots best for you and learn witch ones to stay away from, some guys shoot three shot groups when testing, I personaly shoot five, it helps to sort out flyers and human error, do not be afraid to retest if you have any doubts, I don't know what platform you are shooting, assuming it's a .223 cal a 100 yard zero should be easy, but to tell the truth I just started playing with small bores myself so you will want to look at some ballistics tables for that round and find out where it zero's, so you know how far out you need to put your target to start the sighting in process. Hope this helps.
What twist rate do you have? Assuming it is a "New" rifle, it should be a "fast twist" barrel 1/7 (Colt), 1/9 (most others). Try the Winchester 64gr power point for serious work and their 62gr FMJ for plinking. I find the Win PP load to be excellent in both my AR's.