Low Pairs

It depends on your stack size, position... but most of the time if you are deep enough you should set mine.

I almost always try to see flops with small pairs because they are so well disguised when they hit. My experience has been that it's best to call when coming in instead of raising. I set mine my small pairs and almost never call if missing flop with an opponent showing any interest in an over card flop. Maybe not the right way, but it works for me.

is good play just limp preflop and sometimes u get sets

It depends on many factors you must give an example of a specific situation so that everyone can tell you how they would play