Limpers

It depends on the limpers themselve, as well as different other circumstances.
If I am quite deep (and they are deep as well) I tend to ignore their existence and open raise normally (with a small addition for each limper if there is more then one). If there is more then two of them I might reconsider some of my holdings and overlimp them instead, in hopes of a good payout if I hit a good flop.

If I am short, limpers add further dead money and therefore pushing your holding preflop (which you might have done anyways) gets more profitable. As a result, my pushing range widens a bit. If there are several limpers (and if these are frequent limpers) I might even push any two out of late position. Limp/call plays are extremely rare if you push a reasonable amount of chips.

Of course you always have to be aware of traps. If a player with 25/5 stats open limps you can savely assume that he is a fish and try to get most out of the situation. However, if a player with 25/23 suddenly starts open limping you should be very cautious. I really like limping behind in these situations since your opponent will very often hold a KK+ hand. If you hit two pair or better you will very often be able to stack him of.

I hope I was able to help a bit.
If you have further questions feel free to ask!

Regards,
Asaban