It sounds like you need to LISTEN to more music before you venture out and play live. The magic and fun of live ensemble playing is an artform in itself, and can best be learned by listening to bands that play your type of music.

Organs and strings generally sustain, while pianos and clavs are played more percussivly. Brass lines are usually a "hook" that defines the tune - just copy the riff.

The main trick here is no trick at all:
Listen
Study
Practice
Then, get out and have some fun with your skills !