I've worked with a lot of people who are either on or off. They are either on their diet and exercising hard every day or they are off with very frustrating results.
I think too often we get caught up in thinking, I didn't make it to the gym today or I ate a cookie (or two or three) and all my weight loss or healthy living plans are done. This becomes especially hard during the holidays when we're too busy to exercise and there is so much good food around. I find myself thinking, I'll worry about it in January!
But living healthy is not an all or nothing propisition. It's possible to be healthy (and meet those weight loss goals) by just doing the best we can each day and making small changes that will add up to big results.
I always recommend just one small change a month. It can be something as simple as, drinking eight cups of water and cutting out one soda or scheduling three exercise sessions a week on the calendar (but not getting frustrated if we don't make it). As the months come and go and you keep adding a new healthy goal each month (and hopefully the previous months' goals have become a part of your lifestyle) you will see amazing results and not feel like you're completely changing your life or seeing the yo-yo effect of being all or nothing.
The most important thing is to not give up. Wake up each day excited to make healthy choices. Don't beat yourself up if you aren't perfectly healthy. Remember that we're not trying to lose seven pounds in a week or something ridiculous like that. We're making smart, healthy choices that will help us to feel good and look good for a lifetime.