One thing I've noticed about a lot of guitarists is that hand size simply does not matter. Doug Wimbish, Alexi Laiho, Rusty Cooley and Marc Rizzo all have small hands. At least no bigger than mine.
Here's one of the cool little finger flexing exercise that John McCarthy uses with his students and you can find it most of his lesson videos. John said you should do something like this every day to help your fingers stretch out and exercise each one. It will help you with coordination especially with the middle finger and your pinky.
Use a metronome to keep tempo. Start at a tempo that is comfortable and easy for you to start with. Don't worry about speed, as you get a comfortable feel for the exercise at a reasonable speed then you can increase the tempo of your metronome a couple beats and work at that tempo until you get the new speed down pat. It's recommended that you do something like this for about 5 minutes of your practice.
If you start to feel pain stop the exercise and go onto the rest of your practice session. Follow up with the finger exercise the next day and try and play the whole 5 minutes again.
By following the example below it will help you with those riff and licks that you have problems reaching with your fingers.