Al Green

The key to playing a nice bass part on this song (or any pop song with vocals), is to play something that supports the vocals and grooves with the other instruments as well.  It's as simple as that.  Listen to the singer's melody and the rhythm of the drums and try to bridge the gap between them and bring them together in a way that you see fit. 

On this song, I did not play exactly what the bass player on the recording is playing (although he is great) because I wanted to make up my own part.  Feel free to experiment and make up your own parts on songs too.  Don't get me wrong, it is helpful to figure out other people's bass parts note for note sometimes as well, but if you want to make up your own part and supporting the melody and rhythm of a song is your number one goal, then go for it.

Al Green - I'm Still in Love with You