A sensible plan would have you lose about 15 to 20 pounds in 3 months, so between 1 and 2 stone. Weight loss is an overall process and there are no magic answers. Pay no attention to weight loss supplements and pills and all the latest fads. You need to think about many factors but most of them are related to issues we've known about for a very long time. There are many sensible things you can do that will make a tremendous difference over the long term if you need to lose weight. It can be done in a healthy way. This is what has worked for me.
Keeping a food journal really does help. It will give you a much better sense of how much you are eating, and when, and why.
Make a few additional small changes - walk everywhere, always use stairs instead of elevators, walk on escalators, get up and move around at least once an hour if your work or your life in general is sedentary, walk every day, use a pedometer. Walking 10,000 steps a day is a really good idea. Build up to a long brisk walk everyday, or most days. Be more active and watch less TV and spend less time on the computer. Buy one piece of exercise equipment to have at home and be strict with yourself about using it. Sometimes you can find mini-steppers or exercise bikes at second hand stores and thrift stores for just a few dollars.
Start a weight lifting routine. Join a gym. Possibly you can find one that has someone who specializes in weight lifting programs for beginners. Weight lifting will increase your metabolism as well as improve posture and appearance overall. Even if you can't get to the gym you can work out at home using things around the house. Invest in a good weight training book. The Dummies series actually has a good one.
In terms of diet, cut out or reduce things like junk food, pop, fat, fast food. Eat more fruits, vegetables, whole grains, lean meat, fish. Particularly if you choose a vegetarian lifestyle include natural peanut butter, hummus, dried fruit and nuts. Pay close attention to getting the nutrients your body needs to be healthy.
Make your portion sizes smaller. Use a smaller plate - in our society we have become accustomed to thinking that we need a large plate of food at every meal, and we don't. About quarter of your plate of food should be protein and at least half of it should be veggies.
Learn to count calories. At your current weight and activity level, you may possibly need about 2000 calories or more to maintain your current weight. So you will lose weight at a reasonable and healthy rate if you cut back to about 1600 or 1700 calories a day.
Eat small amounts frequently, rather than three large meals. Never skip breakfast. Include some protein in your breakfast. It will help get you through the day.
Drink plenty of water, at least 8 big glasses of water a day, and more if it is very hot, if you sweat a lot, or if you are exercising intensely, and eliminate fruit juices. Fruit juices have too many calories, so get your vitamins from fresh fruit, not the juice. You will begin to see changes in your body.
Vary your routines. Don't eat the same number of calories every day (vary your calories from 1400 a day to 1900 or 2000 some days), eat a variety of foods, and do different kinds and amounts of exercise. You will lose weight much more efficiently if you mix things up from time to time so that your body doesn't adjust to any one routine.
An area that many people overlook is getting enough sleep. You are much more likely to overeat or to binge eat if you are tired and not well rested, so get enough sleep.
Check out websites about nutrition, exercise, weight training, etc. Here are a few helpful links.