I find that even after years of playing my left hand tension is way too much to get any decent speed I think I just anticipate quick passages too much and tense up. Has anyone got any tips for getting rid of tension in the left hand/right arm?
(Im assuming you're a right handed guitarist).
For your left hand id be looking at your thumb positioning, do you wrap it around the neck?

For your right arm there could be many possible problems. Do u pick with your wrist or elbow? If you speed pick using your elbow, stop, start over and learn to use your wrist. If you already use your wrist, you may be anchoring. Anchoring is a very common practice that causes excess tension in the picking hand and forearm. Theres already alot of threads on this topic if you want to look into it further.
Yeah I'm right handed, I do use my thumb over the neck a lot but thats the way I play I use my thumb for chords. I definitely don't pick from my elbow or anchor a finger, I rest my right palm on or near the bridge as a mute and anchor. I get pains in my forearm on the right arm though... I'll look into the other threads thanks.
Alot of it has to do with muscle memory, too. We all have really fast stuff we want to play and we're really anxious to do it. The key is slow and easy.
Learning it at a really slow speed is the trick. Is it boring?? Absolutely. You wanna be blazing away, and this just isn't it. But again, it's all about muscle memory. Your fingers are mindless slaves...they'll do it right or wrong, they don't care. If you learn it right slowly and repeat it alot, they'll do it right for you when you speed it up.
When you go over something really slow, you can find the points where you have tension. If you have to, stop right in the middle of what you're playing at the exact moment you feel the tension. See where your fingers are and try to pinpoint what's causing the tension and focus on relaxing it or changing your hand position to where there is no tension.
We all learned to write by tracing over the dotted lines until our hand got used to forming the letters...muscle memory. Now you do it without even thinking about it and at a pretty rapid speed. Same theory applies here.
Good luck to you!!