I can't remember the last time I made a New Year's resolution, but I have made resolutions mid-year and kept them.
Mid-2011, I resolved to learn George "Rhino" Thompson's Verbal Judo, as much as a means of self-discipline as of more effective communication.
Mid-2012, I made a daily commitment to three sun salutations after hearing they were part of Dr. Mehmet Oz's morning routine. Slowly but surely, they have improved my flexibility and weight. I've added some qi gong, reverse pushups, Figure 8s, and medicine ball work in a 20-minute continuous flow that kept me from feeling stuffed over the holidays. If I don't have twenty minutes, I just break the routine down and do one exercise.
The pressure to make and then keep New Year's resolutions is external. Internal resolve leads to more lasting results.