They should be the same thing that motivated you to lose weight in the first place. And if that wasn't something solely for yourself, then it's not likely to have a large impact to keep you going. If you were motivated for your health or to enjoy your time better with your family, a reason that can keep you going and not a here today gone tomorrow one, like maybe a boyfriend, then that motivation is still there. You just have to keep reminding yourself of that reason you first decided to lose weight.
You can do small things to help push you, but the motivation is really what made you want to lose it to start with.
Some of what I did along the way was to picture my favorite actresses tummy as being MY tummy.
Course I wouldn't mind looking like Julia Roberts all around, and not just in the tummy.
I also bought an outfit that was more expensive than I would normally buy, and a size smaller than I wore. I hung it on the front of my dresser so I'd see it daily, have to move it to get into my drawers, and would try it on daily until the darned thing fit. LOL Then I'd go buy another one.
And the best way to stick to it...get all the junk out of the house. If you have a spouse or parents, which might make that impossible, try at least relegating your healthier foods to a separate cabinet and fridge shelf. That way you don't have to look at the other stuff, so it doesn't tempt you.