Resistance training (weights) is essential to weight loss or any good fitness program.
To get started, you need a basic program that covers all body parts, example:

Shoulder Press - shoulders
Bench Press - chest
Lying pullover - lats
Seated row - upper middle of back / lats
squats - front of legs
leg curl on ball - backs of legs

Now that we have identified the exercises, we need to establish the weight - choose a weight that you can do 18 repititions of (the last 5 / 6 should be difficult).

Work through each of the exercises with the appropriate weight and when you have completed all exercises once, repeat another once at first and then progress to repeating twice.

Resistance training will help to build muscle mass and burn fat - your metabolism will be increased.

This program combined with the cardio program from Tip #1 will now start to help you lose calories, increase metabolism, build muscle mass and lose fat.