Orange dots against a black background work great. I use the 1" size at 100 yards; the 3" at 300;the 6" at 400-600 etc.
The targets like Canazes posted are great, too. Important thing is to hold small enough to minimize drift,canting, and reduce wiggle.Some scopes have thinner reticles than others. Suit aiming points to the reticle and force yourself to "hold small".
Lots of styles work. But if you are holding against something too big you may tend to move around in it too much.
