I've always maintained that to be a good rhythm guitarist one must be creative, yet decisive.
A chart may be something as simple as.... G / / / C / / / Em / / / D / / / .... and a good creative guitarist could find a hundred or even a thousand ways to play through this progression. But to find a good part fast that works with everything else around it, that's a skill. To do it quickly. That is art.
Years ago I worked with session ace Michael Thompson and was amazed at his skill in this area. He interpreted the chart in front of him almost instantly. Reading it, coming up with a part and a tone all in the time it took me to pick up my pick. Humbling to say the least. But I made it my goal from that point forward to be that guy who could come up with the prefect part and tone quickly. Not there yet, but I see shades of it every now and then.
One of the keys is to be a fan of music. Different styles. Be a voracious listener. But just listening doesn't make you creative. Try to think like they thought to create. Learn the creation process, not so much the mimicking process. Also the more listening to great music you've done the more likely you are to recognize the tone when you've dialed it in.
One of the best things you can do is write, write, write. Write, record and arrange. Produce. For every track I play on for someone else's CD or film or TV Show, I probably record a song at home, or at least an idea of some kind. A lot of times my experimenting at home ends up on tracks for others.
Most guitarists spend 95% of their practice time on soloing and only 5% on rhythm. But when one gets out and plays or does a session the inverse is the reality. 95-100% of your time will be spent on rhythm not soloing. The busiest players are the ones who realize this truth.