Start the weight loss process by determining how overweight you are taking into consideration your height. There are different tables that can help you with that. Search for "healthy weight charts" on the Internet to find them. This will help you to determine how much weight you need to lose to achieve a healthy weight for your height and also to set your goals right. For example, if you weigh 200 pounds and your height is 5'6" you are considered to be severely overweight. The normal weight for your height is within the range 106-156 pounds.
However if your height is 5'10" you considered to be just moderately overweight. The normal weight for your height is within the range 125-175 pounds.
The other things to consider are your muscle mass and body frame. If you have well-developed muscles you will weight more but this weight comes from muscles not fat. If you have thick bones you might not reach the lower limit of the range. In this case the extra weight comes from bones and not fat.
Another tool to determine if you are overweight is to use the Body Mass Index (BMI). You can use a chart or the formula to calculate this. Charts and calculation tools are freely available on the Internet. Here again if you have well-developed muscles this will not work for you since your extra weight doesn't come from fat.
After determining how mush weight you need to lose you can set your weight loss goal. Consider using 1-3 pounds per week and set a realistic deadline. Take a picture of yourself. Also take the body measurements such as your weight, size of your chest, waist, hips, thighs, upper arms. Take measurements every week to track your accomplishments.
If you engage in vigorous strength training some measurements (upper arms, for example) will not change or might even increase however this will be due to muscles not fat. Keep a weight loss diary to record all your weight loss activities such as food you eat daily, exercise, supplements taken, relaxation and visualization exercises as well as your energy level and other details. This will help you if you reach a weight loss plateau or don't lose enough weight weekly. Also write a motivational letter to yourself - this will help you later on when your motivation level decreases.
Following these techniques will ensure that you set a realistic weight loss goal and have all the tools to achieve it.