When beginning a diet, set realistic weekly and long term goals. Like with any other project, if your goals are unattainable, then you have no chance of success. Even if you are trying to just drop 20 pounds in too short a period of time, you're just setting yourself up for failure. Instead of setting such an unrealistic goal, give yourself more time and set a goal that you may be able to attain for that specific week. Stop focusing on the big picture. Think about your weekly weight loss instead.
During each meal, pause for a few minutes. This will give your body a chance to let you know if it is full! Just remember to make stopping for a few moments between courses a regular habit. Take a break for a moment to see how hungry you really feel. Adjust the amount you're going to eat accordingly.
Cooking all your meals instead of eating out is a way to cut calories and lose weight. Most restaurants serve meals that are over 1,000 calories; that's almost a whole day worth in just one meal! When cooking for yourself, cook low calorie meals that are also low in fat.
Exercising is the key to changing your metabolism to achieve a weight loss vs. a weight gain. If you can't afford a gym, there are tons of videos available that you could rent or purchase. Start with the basics for the first few weeks, while your body gets adjusted to this new wonderful lifestyle.