Resolving that you won't have any alcohol keeps the focus on the alcohol. Instead of focusing on what you don't want to do, focus on the positive aspect, like drinking more water.

Use gratitude and other positive emotions to steer your mind out of any pitfalls.

Changing your environment helps you keep away from temptations and the risk of falling out of your commitments.

For example: If you have candy near your desk, you are more likely to eat it.

There will be obstacles and sudden changes in circumstances that will hamper our self-commitments.

Have alternatives and back-up plans in such cases, to avoid indulging in something sinful or skipping your workout. Anticipate situations that may occur to help yourself formulate an alternate way.

Starting small and building on the same leads to early success. Our good habits also have a way of spreading in other areas, if sustained long enough.

Example: Avoiding sugar and gradually succeeding in it, builds willpower to moderate caffeine intake.

Visualizing your rewards and consciously feeling euphoric about them improves your chances of engaging in the actions that result in those developments.

There will be hurdles and setbacks in the quest of trying to make yourself healthier.
Being harsh on yourself if you miss a day, or indulge in something you are avoiding will do no good. Accepting that you are not perfect and treating yourself with love and care is a much better strategy than being self-critical.