There's as many different ways to collect as there are collectors. Some years or mint marks may be very scarce and command quite a bit of dough. Type set collect one example of each type coin. For United States coins this is sometimes further subdivided into 20th Century Type Sets, etc. Indian head cent, Lincoln cent with wheat sheaves reverse, Lincoln cent with Lincoln memorial reverse, and some might want to include the new copper-plated zinc cents.
Themes collect anything with a specific image or theme to it.
Accumulation look around and just buy what pleases you. Remember, you should purchase a coin because you find it pleasing aesthetically or historically. Anything you make as profit when you sell is simply icing on the cake. Crowns of the world crowns are the basic denomination of a country. Try to find as many countries as you can.