aiight say you have a sample that has the bassline you want in it (with all the other instruments in it whatever...) you'd definitely use a filter to get rid of as much of the higher frequencies as you possibly can (sometimes it sounds better if you leave a little bit though). After filtering it, you may try some eq as well but thats not entirely necessory until your in the mix down process and trying to get it to sound good with your drums. What you want is compression I believe. You want to bring the overall level up and give it punch. The best way to get basslines is to get 3 or 4 different notes from that bassline (if the sample allows) and make sure its all filtered, compressed and eq'd whatever... than you can recompose your own bassline using different combinations of pitch shifted notes and what not.

The exact process I described can be heard on the beats "Hip Hop" and "Smooth Identity" on my soundclick page.

Hope this helps,

Peace

www.soundclick.com/5thsequence