Hold the guitar at whatever position is most comfortable for you, not at whatever looks the coolest. I found that I got less fatigue in my forearm when I was playing sitting down, so if I have to stand when I'm playing I use a short strap like a jazz player. Not the coolest looking but it takes the pressure off the tendons and allows me to play a lot faster and cleaner. Akira is also right, soaking your hands in warm water helps a lot too. I just recorded in a studio which was like an icebox, I soaked my hands before every solo, made a big difference. Also, don't crack your knuckles or wrists, it's not good for your joints. Cod liver oil capsules and chondroiten are also good for maintaining joint flexibility. Also, if you're playing something that causes your forearm to burn, take a break for a few minutes, shake your arms and allow the blood flow to carry away the lactic acid.