For me, its to really listen to different bass players and seeing how they move around on the bass and being able to replicate that. Its always the little, subtle nuances that really make your arrangements stand out. Then also, I play actual key/synth bass differently than I do when trying to replicate and actual live bass sound. Darrell Freeman is someone that I listen to not for how he plays live bass but he is also a beast on key bass (ie. One Thing - Marvin Sapp (Diary of a Psalmist).
I am a Reason Head so I use the Reason Bass refill which is amazing. It replicates some of the well-known and much used basses by using high quality samples and including effects such as slides, mutes, and picks. Its pretty cool. Don't get me wrong, I love having a live bass player on my music but when you cant find one, that is my goto.
thanks, thats some good advice. Like you said, its the little stuff that makes a difference.