One thing I remember when I first started was not getting the concept of muting certain strings. Like, playing a simple G or E chord was no problem but when it came to a D, I couldn't get it through my thick head that you weren't supposed to play the 5th & 6th strings. Just a stupid little misunderstanding like that and it delayed me for about a year cause I gave up on even trying. It always pisses me off when I realize that if my beginners book had explained things just a little bit better, I wouldn't have wasted that first year leaving my guitar in the closet.