[quote name='JamesBass' timestamp='1364340057' post='2025261']
If you get a squash ball, place it between your thumb and fingers and squeeze, do that for 5 reps, as if you were in the gym doing weights and then change finger and work your way through that a few times, you'll be surprised at how much stronger your fingers will get and the quicker you can do it the better as well for agility on the fret board.
Also adjust your strap so that when you are playing stood up your left wrist isn't bent too much as you'll cause some problems with RSI and the like. As with anything make it comfortable for you and just practice and practice and practice! A good exercise I do/came up with is running up the neck on the G string i.e; 1st finger 1st fret up to the 4 fret, then jump 4th finger 4th fret on the A and proceed down, then 1st finger 1st fret D and up the neck, 4th finger 4th fret on the E and down the neck, try and make it OFPF if you can't then just do it till you can, do that a few times in your warm up and you'll soon have the hang of it!
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~+1 This. You can also buy a finger strengther aimed at climbers I think which will help. I've flirted with tennis elbow (that's where it hurts on the o/s of the elbow) which I'm pretty sure was caused by going hard a a finger per fret with the guitar slung too low. I guess the answer is to keep the position comfortable and stretch gradually.