If you have been playing guitar for more than five years, and have reached an intermediate level, chances are that 90% of your mistakes are from your picking hand. Most teachers and players ignore the importance of developing the right hand. We have a tendency to think that the left hand is doing the work and the right hand will take care of itself.
If you watch any great player, no matter what style they play, their right and left hands are totally synchronized - and they make it look easy. I have my students work on separate right and left hand drills from day one.
If you have a drum machine, set it to a basic rock or blues rhythm at about 90 beats a minute and pick the open A string to the snare on beats 2 and 4 (if you don't know what a snare sounds like, listen for the loudest drum). When you find the snare and can hit the beat without thinking, find the bass drum and hit the low E string to that. Later, you can move the tempo up and down, and even switch to different styles of music. This is a great way to warm up and feel the pulse of the music.
Another exercise is to find a beat, strum all six strings muted, and switch between 8th notes and 16th notes every other beat. Make sure that you are keeping time with the music. The better you get with this, the easier it will be to play with other musicians.
The students that I have that do these drills improve a lot faster than the ones who don't. You can't fake rhythm. It needs to be second nature to you, and feel natural. Anyone can develop good rhythm chops if they work at it.
Mike O'Malley's instrumental power trio is called No Walls and their latest CD is entitled "World Abroad". He has been playing guitar for almost 30 years and graduated from Music Tech in Minneapolis in 1988.
O'Malley currently has 45 guitar students that range in all ability levels and styles.