If you want to lose weight one of the best ways to help is to break down your bigger goals into smaller ones. Losing, for example, twenty pounds is a big challenge! After all, in a healthy world you only really want to drop 1 to 3 pounds a week. That means twenty pounds should take about 10 weeks.
10 weeks is a long term goal. It sounds so achievable at the beginning. That 10 weeks seems so far away that you are very likely to "take it easy" because you "have plenty of time!" Four weeks later, when you have been very lax on yourself and if you are lucky you may have dropped a couple of pounds. But now you have 6 weeks to lose 18 pounds! That's on the upper end of healthy and now it's a very hard to achieve goal!
So how should you break this down. Well it depends on you. I've found four week intervals to work the best. Four weeks is just long enough to give myself a little leeway for lapses in my goal, while simultaneously giving me the kick in the pants that I "ONLY" have a few weeks left! In addition it allows you to use another mind trick: the "I can do it for X" mind trick, because after all it's only a month, you can be super strict for a month!
By the time the end of that month rolls around hopefully you will be so well on your way to your big goal that you will just let it keep going! After all you already showed that you can be super strict for a month, and it wasn't so bad! So break up your big goals into incremental smaller ones. Gauge where you are when you get to that smaller one and adjust accordingly. Losing weight and keeping it off is a bunch of incremental changes over time! Going for the big bang is dooming you to failure before you even start.