Changing bad habits

I am just wondering what process people go through to change habits?

I'm working under the theory that it takes 30 days to make or break a habit. So I have been focusing on one habit a month. For instance, in January I focused on add regular exercise to my routine. For me, it was exercising everyday. In February, I added eating less salt. March focused on eating out less. Etc, etc. Basically, the idea is to keep everything else the same and focus on one thing. Each month you add something new and hopefully what you did the month before became the norm. So in March, I exercised everyday, ate a low sodium diet, and did not eat out.

The idea is to change all the bad habits you want, so by the end of the year you accomplished a lot without feeling like you have been deprived.

Thoughts?