When I first started, I didn't have my own guitar, which meant I was moochin' minutes on any axe I could lay my hands on. 'Trouble is, I had no concept of the importance of correct positoning of my hands. To make things worse, my hands weren't as strong as they needed to be. Most of the guitars I had access to were acoustics with heavy bronze strings, so I got used to cradling the neck in the web between my thumb and forefinger. I still do that unless I make a conscious effort to put my thumb at the centre of the neck, where it belongs.

I've been playing for over thirty years; the best way I know of for breaking bad habits is to identify and correct them as soon as they appear. Teaching yourself is not going to do this for you. Get some lessons from someone who has the experience to recognize potential problems before they become habits.