Watch the The Importance of Good Time online guitar lesson by Allen Hinds from Melodic Improv
If I were to pick out one common denominator that all of my best students have, I would say it would be having good time. And if you think about it, 99% of what you do will be with an ensemble, so having good time sensibility is really something special.
When I have a student who doesn't have good time, it's often because they aren't moving. It can be as simple as tapping your foot - if you think of the greatest rhythm guitar players, often times they're dancing with the music. A way to improve is to record yourself and listen to yourself playing. You'll hear the areas that you need to improve in, and find new ways to compensate for areas that you're having trouble in.