Achievability is the third part in goal-setting. Don't try to do too much at once. Small changes are lasting changes. You can make it a goal to make one small positive change every week. Make small goals that you are able to achieve, and reward yourself for meeting each one.
Nothing succeeds like success.
Realistic doesn't need much explanation, I think. Don't set unrealistic goals for yourself, like losing 10 lbs of fat per week, or increasing your bench press by 100 lbs. in a month. You'll be disappointed and lose motivation. Time limited refers to setting, well, time limits on your goals. I suggest you make a variety of goals for yourself for each day, workout, week, and month, with varying expectations.