Eva's articles should help you immensely. If you are still having problems good photos (by you or off of Google) of the bugs will help us identify them for you. Descriptions of their size (a few mm, cm or grain of rice sized, etc), movement and identifying features (legs, antennae, tentacles, etc) will help us identify your bug.
One of the important things to consider is most tank animals are completely harmless and actually indicate that your water quality is good. Often these little guys need excellent water parameters to flourish to visible levels. Usually these guys are in your tank but not in quantities where you can easily find them and levels of the critter will eventually adjust.