The advice on weight loss doesn't change much--eat fewer calories, move more. Doing it is the hard part.
Here's a way to reduce some calories and certainly fat. Instead of using a bottled salad dressing or even an oil and vinegar mix, take a packet of Splenda or Equal (I haven't tried any of the others) and sprinkle it over your salad. Then take a fresh lemon quarter and squeeze that over the top. It gives you a sweet/sour dressing taste that is really quite pleasant and even wakes up the taste of those bagged salads. Add a little pepper if you are so inclined and you'll have saved calories and fat.
Now as some of my favorite movie characters say, "Move it! Move it! We got to move it, move it!"