Growing up, my theater teacher told us every rehearsal, "practice doesn't make perfect, perfect practice makes perfect". When you first start playing guitar, it can be tough to overcome finger and wrist pain as you develop hand strength and dexterity. As you deal with pain and fatigue, you can develop poor posture and technique, which greatly hinders your long term growth as a musician. Here are a few simple things you can do to be proactive about the beginner blues so that you can get the most out of your practice time.
Warm up (whole body)
Playing guitar utilizes muscles in your arms, back, core, and hands. Start your practice time after a run or workout and stretch your back, arms, and core before picking up your instrument. The increased blood flow greatly reduces fatigue.
Drop your elbow (fretting hand)
When starting out it's easy to push too hard on the strings with your fretting hand. If you have proper hand position with your thumb on the back of the neck and your fingers parallel to your thumb, one easy way to reduce fatigue is to slightly raise your guitar neck towards yourself and drop your elbow a bit. This allows your arm to act as a counterweight relieving some stress on your wrist and fingers.
Follow through (strumming hand)
Strumming is a complex movement and if you lock your elbow while strumming your wrist can get tired quickly.. Try lowering your guitar strap a bit and following through with your whole arm as you strum. It's ok to over-exaggerate the movement at first and look a little silly to get used to it, but a subtle follow through can greatly reduce wrist strain.
When you are really engaged in learning a song as a beginner, it's easy to try to fight through the finger pain and try to power through the hurt. Your body needs rest as your fingers will form calluses over time. Overplaying can cause your new calluses to tear, which results in the formation process to take even longer. Also, you're much less likely to practice consistently if you take several days off to wait for your fingers to heal from a torn callus. The best way to manage finger pain is to practice consistently every day and stopping when your fingers begin to hurt.
Sit up straight (back)
When you are first starting out, it's easy to hunch your shoulders forward so that you can look at the fretboard while you play. This puts tension on the core of your body while you're playing. Instead of hunching forward, slightly angle your guitar towards you so that you can see the fretboard and have proper posture.
Change up your pick (picking hand)
Many new students struggle to hold onto a pick while strumming or picking and overcompensate by pinching down on the pick tightly. This can lead to hand fatigue and muscle cramps over time. If you have a slick plastic or celluloid pick, you might want to change to one with a rougher texture. You can also wrap a small piece of masking tape around the top of the pick to give yourself something to hold onto.
Lighten up your strings (guitar)
If your fingers are getting shredded by your guitar strings, you might consider looking for a "silk and steel" folk set for your acoustic guitar or an ultra-light set of strings for your electric guitar. Silk and steel strings have a steel core but are wrapped with silver plated copper and silk which is much easier on the fingers. For an electric guitar, thinner strings have a lower tension and are easier to press down.
That's it, if I can answer any more of your questions, shoot me an e-mail!