You know, that's a very big question. I guess the very first thing is to define what you want to collect. Again that's going to be another big question. One very very very, and I cannot help to insist on this point is when you try to get hold of silver coins that you may think it's a good deal.
Examples like the early American silver dollars like the 1804 dollar coins and quite a fair bit of early Asian coins that are counterfeit aren't minted in silver but some other metal. By color alone you can tell the differences between a genuine one and a counterfeit one.
Of course there are many other ways to tell, such as looking at the fine details of a coin and mass, which can possibly help you out.
Well that is a very brief and generic thing I typed out... I hope someone else will be able to point you in a better direction.