New Years Resolutions are overrated, with failure rates pretty high. Instead last year I opted for 101 Things in 1001 days or Day Zero Project. The idea being that you create a list of 101 things you want to do and then spend the next 1001 days doing them. You're far more likely to get a great number of them done because you don't have to start immediately. There used to be a good website for keeping track of yours and other people's 101 things, but it seems to have been down for a while.
I've pretty much given up on my list after a year working on it, but in that time I've achieved quite a lot and got so much benefits from the things I've forced myself to do.
The year before my resolution was to say Yes more. I'm still saying Yes more than I was, which is leading to a lot of fun and worthwhile achievements but is taking up a lot of time.
I'm toying with doing Rejection Therapy this new year, since shyness stops me from going out and selling myself. I'm rather scared to commit to a whole month of it though.