I think have a goal in sight, or something to aim for in the short term. If you have ten stone to lose, but really want to lose one of them by your birthday and wear the dress you haven't worn for years on that night, then that's a more motivational goal than looking at the ten stone, or the 'where I'll be in two years when I'm finally at my target date' as a whole.
I always have something to aim for, for example in December 2010 I didn't go to my office Christmas party, it was at a golf club and involved wearing a dress in front of numerous stick insect colleagues, and I just couldn't be bothered with feeling that level of self-consciousness for a whole evening. Every time I went to eat something questionable last summer, I thought about the Christmas party 2011 and it helped a lot.
I'm not much of one to preach having spent the last 6 months gaining constantly, but I actually put that down to having nothing to aim for. I didn't make a conscious decision in my head to 'get to there before then' I just carried on thinking 'I'll start next week'... until I booked a holiday!!
I am thankfully now well back on track, but with only the target of the beach to thank. Even if I didn't have a holiday though (like the previous 11 years) I would still consider this the best tool out there for me. Being able to wear something nice(r) at my boyfriend’s birthday last October was another small personal milestone to go for, so it’s not always about (NON!)-bikini bodies
I always, always, keep an obsessively thorough food diary too, but that in conjunction with a mini-target seems to be the key for me