General things to look for fairly easily could include wrong diameter, wrong weight, wrong manufacturing method, and wrong alloy. Also, consider the source of your coin purchases. Of course even the best sellers sometimes make mistakes, but you should avoid sellers of multiple fakes.
Down the road, consider posting some of your purchases here on CCF and perhaps we can help you.
"If you climb a good tree, you get a push."
"The danger we all now face is distinguishing between what is authentic and what is performed."