It is extremely hard to get over negativity. It is a pattern that once adopted it is really really hard to overcome. I think for me what helps is trying very little goals that sounds almost trivial, like finish a book, or join a reading group, or like learn something new.

Once I achieve something I feel positive of achieving more. The trick is to start with baby steps. Also friends help on this process but to be honest most people are kind of negative and while you need some cheering in the process, it also feel nice if you have to be in the position of being the positive one for once. It is hard but it put you on perspective to realize how everything is really relative to the point of view you adopt.