Re: Things to know before learning the guitar?
A nice guitar is far more fun to play than an average one. I played a $5000 guitar a few weeks ago and couldn't believe how beautiful one single note sounded on this thing.
New strings are awesome. Restring often.
Learn how to strum properly (look for a video)
DON'T ANCHOR YOUR PINKY ON THE BODY OF THE GUITAR WHILE PICKING
If you're playing metal, don't scoop out your mids and don't use too much gain. If you're not sure if it's too much, it probably is. Make it sound good on clean before bringing in distortion. Also, don't use flimsy weak picks. Get something fairly solid. I use the small Dunlop Jazz 3's for metal and other ones (can't remember the size) for music that is more "strummy".
Don't set up your amp tone while playing by yourself, make judgements based on what it sounds like with the rest of the band playing. Crash cymbals + distortion sound pretty horrible in the wrong hands.
If you're using distortion, mute any string that isn't meant to be sounding, ideally in two spots, or you'll be hitting harmonics and sound like a bowl of cold soggy bread.
Learn the basic chord patterns to suit whatever key you're playing in - major minor minor major major minor minor (or diminished? either seems to work). Makes it more fun to jam away on your own.
The minor pentatonic scale is easy and fun.
As a drummer my 'nightmare guitarist' is one who can't play as well as I can (which isn't very well because I don't practice, I'm a drummer!), doesn't focus on playing cleanly, and can't recognise when his tone sucks. Tone is god.