Before I delve too deep into this discussion, you should know that what I'm talking about here may not have any medical or anatomical basis (for the most part, it's really just common sense). Nevertheless, I will share my experience with you in hopes that it will help you avoid guitar-related injury.

When breaking in a new guitar, perhaps the most important thing to beware of is injury. Maybe you don?t remember the first time you picked up a guitar, but I suspect that your muscles were making all kinds of adjustments in the first few weeks. Let's face it - playing guitar in itself isn't entirely natural. Yes, there are those of us who pursue virtuosity, and those of us who strive to make the guitar an extension of our body. However, most of us are also aware of the fact that the techniques we perform on the guitar are physically unnatural; but we're not always in tune with how our bodies are going to react.

My experience with breaking in a new guitar is that my muscles attempt to make all kinds of adjustments (usually this means weakness and pain in the wrist and forearm). Why? Because every guitar is unique. Even if the guitar in question is the same make and same model, it's bound to be different in subtle ways. Most importantly, the neck and the action are going to be different.

Just recently I picked up a new acoustic guitar. I am an electric guitar player first and foremost, so switching to an acoustic meant altering my technique. I think that this is a necessary evil. Compromise and sacrifice aren't inevitable; it's just a matter of tweaking your technique to better suit the guitar. In any case, 5 days after buying the guitar, I was suddenly haunted by pain in my wrist and my forearm (the fretting side). Then I remembered that this happened the last time I bought a new guitar. Then it dawned on me that my muscles were trying very hard to catch up.

When I had that pain in my arm I could barely type let alone play guitar. If you find your arm in a similar condition, then I highly recommend resting it. If you proceed to practice with a damaged arm, it is sure to be problematic. Rest your arm for a day or two, and it should restore itself (otherwise see a physician). When you really sit down and think about it, it makes sense. Most people aren?t going to (and shouldn?t) run 10km the first day they start an exercise program. If they push themselves too hard, they may injure themselves. Guitar is the same in many respects.

In summary, here are a few things to remember when breaking in a new guitar:
- Stretch your fingers, your hands, and your wrists before playing
- Take your time with the new guitar - don?t try to do too much at once
- If you?re not in the habit of doing warm up exercises, do them

Fundamentally, guitarists really shouldn?t be practicing more than 30 minutes to an hour at a time if they want to avoid permanent damage (especially if you have a habit of playing with bad posture). This doesn't mean that you can?t practice several hours a day, it just means that you should take breaks regularly and live a balanced life if you want to be a well-adjusted musician (and I suspect that most of us hope for a long-lasting and enjoyable music career).
i don't think the title fits... your not really breaking in the guitar your breaking yourself into the guitar... if that makes sense
If you want to shine like the sun first you must burn like it.