Try again, and this time consider the following tips:
1. Be realistic. If you're trying to lose weight, set your sights on losing no more than a pound or two a week. Don't try to lose it all in a month. Also, know that you're human and prone to setbacks. Don't let a failure to stick to a plan derail you from picking up and trying again.
2. Be specific. Don't say you'll exercise more. Instead, commit to walking 30 minutes during your lunch break three days a week. Whenever possible, take the stairs; it's free exercise, and every little bit helps.
3. Find a buddy. It's almost always easier to get any goal accomplished if you have a partner who's trying to accomplish the same thing.
4. Log your progress. Writing down how much you've walked in the past week gives you a sense of accomplishment-- and the encouragement to keep going. Also, it helps you to spot before they impede your overall progress.