I find with myself it helps to start at the beginning of something. Like the beginning of the month? Luckily we have a new month coming up right away
Start calling November your "Month of Healthy Living". When I went back to school this fall I knew I would be temped by all the junk I used to eat when I was in school, so I started call this "My Semester of Health". I'd joke about it with my friends, and then if I was temped to buy something they'd say "But what about your semester of health?" and it would keep me in line.
Maybe journal your progress? I love my little food diary (and my blog here on OD).