Have you ever seen men who seem to have breasts? They don't look overweight but they have fair sized breasts. I can only imagine how self conscious they must feel. I am sure these men have noticed them as well and have tried to think of ways to reduce them. Man boobs can be caused by more than just fat deposits in the upper chest area, they can be caused by hormone imbalance, medication and diet.
First you have to figure out why the man boobs developed in the first place. It you are overweight than that could be the obvious reason. If they seem to have just developed over a period of a few months or a couple of years than it could be gynecomastia. This is a medical condition that causes men to develop large mammary glands. Men inflicted with this can actually start to secrete milk from their breasts. This is obviously a high source of stress for every man who develops this problem. Doctors can only guess at what causes gynecomastia but have recently focused in on an imbalance of sex hormones.
There are some steps to take that can reduce the prominence of man boobs. Men who are afflicted should change their diet and eat more healthy foods. This is not a quick fix but by cutting out junk foods there will be a slight reduction in size over time.
Cardiovascular exercise will burn any excess fatty tissue on the chest as well as the rest of the body. Walking or running at least 20 minutes a day and a minimum of 3 to 4 times a week should start the fat burning process.
Exercise you chest area specifically using a light weight high repetition routine. Inclined bench press, butterflies and push ups would be an excellent routine to start with. This will eliminate man boobs but there will be a reduction in size over time if the exercise regime is consistent.
Exercise and diet are not quick fixes to the problem but you will start to see results over the first 6 months. This can only reduce the appearance of man boobs by so much though as it is not just fat tissues causing the problem. There are man boob specific training routines available from a number of different sources. There are even pills available now that claim to be effective in reducing the size of man boobs but I have never met anybody who has had success with any of the pills offered out there, so this is not something I would recommend.