I tell all my clients to make SMART goals. This is a well-known acronym standing for Specific, Measurable, Achievable, Realistic and Timely (or Time-Bound). I tell people this because the vague statement of "I want to lose weight" or any similar statement tends to yield no results. When we actually think and plan out SMART goals, things start getting done.
I ran smack-dab into a personal example a couple days ago when I picked up my bridesmaid dress for a friend's wedding, which is happening in July. Because the bride is awesome, I got to pick my own dress, as did all her bridesmaids. It's a subtle blue strapless stunner. And it doesn't fit. :P
Due to depression and a number of things, I slacked off on my own diet and exercise program over the winter and gained weight because of it. Not a ridiculous amount, but enough that I've been meaning to go on the offensive with my program for awhile. Until I had a firm deadline, though, I was putting it off. There were a lot of "I'll start tomorrow"s, and "eh, I'm busy today, it's not a huge deal if I don't get my run in." Now that I have a firm deadline in mind, it's actually easier for me to consistently make the right choices to get there. I'm not freaked out about it; just focused. I haven't gone on a crash diet; just adjusted in a sane way and am making sure to get in my cardio every day and working harder on the strength training. This reminds me of how important the components of the SMART goal are.
Specific means you have to know what you're going for. Don't be vague. If it's about weight loss make it a number of pounds or a clothing size. If it's about strength, specify exactly what you want to be able to do. If it's a functional goal, state how many miles you want to be able to walk or run, or whatever.
Measurable means you can quantify it. If you just want to feel better, how will you know when you're there?
Achievable means it has to be possible. Don't set yourself up for failure by making an impossible goal, for example losing 30 pounds in a week.
Realistic means you have to think about how likely you are to follow through and achieve this goal. Even if the goal is possible, like getting ready for a marathon in 2 months, you may not actually be willing to put in the amount of work it would take to achieve it. Think about what you're willing to put into your goal and adjust accordingly.
Timely or Time-Bound was what I was missing. Deadlines help us not to put things off continuously. If there's no event coming up, try picking an artificial deadline. It helps when we have something to hang the deadline on, though. Otherwise we can just keep moving it back.
Try writing your goals out and testing them by these criteria. If they don't fit, tweak them until they do. Then, post them somewhere you can see them so that you can make good decisions and make a little progress each day. Go for it!