Change your environment
The environment you are in has a direct bearing on your self image. If the people around you are mediocre with poor self image it is very likely that you will become like them. If you wish to improve your own self image, get associated with people who are positive, enthusiastic, and energetic. Make friends with people who are dreamers and are growing.
However, be cautious of people who look down upon you. They may look, very successful, positive, and energetic, but they too are suffering from low self image, as a person with positive self image will treat people equally, and embrace anyone who comes to them as a friend.
One great way of creating the right environment is to be around good books, and audio recordings of powerful speakers. This is one of the best ways you can associate with positive people that will do wonders for your self image. Attend motivational seminars and training sessions, as you will readily find a group of people who have decided to help themselves and others and therefore are improving their own self image, and will help you to improve yours as well.
Paint a new picture
What picture of self do you have in mind? If it is one of a positive person, who is energetic, radiant and successful, who enjoys good relationships, and is climbing up in life, then it is a positive self image. But if it is not that, then your self image needs some attention. The painting of self that is in our mind is the one that got automatically generated based on our environment, circumstances and our experiences.
But now, what you will do is to create a painting of yourself, the way you want it to be, consciously. In your mind take the old picture and tear it off or visualize it burning to ashes. Then create the new picture step by step, Make necessary changes till you have the picture of your improved self. Please note it has to be 'your own improved self' and not an imitation of someone else whom you admire.
Once you have the picture ready, you have to start believing that it is what you are from right now. From now on what ever you feel or think, match it with the new picture you have painted. If your thought or action is not consistent to this new improved picture, change the thought. In a few days of making this conscious effort you will see that you have actually become the picture that you have painted.
Correct your body image
If you are struggling with how you look you should evaluate your thinking. Is your opinion about your body realistic? Would a change give you more happiness, self-confidence and success?
Is there something really wrong with your body? Or is it just a mental perception based on your unrealistic expectations and past mental programs. You have to be really honest because a poor opinion of yourself is a barrier to your social interaction with others.
Each one of you has the right to look good and attractive. But first get rid of the stereotyped perception of what looking good is. Of course you need to have a wonderful figure if you are a model or actor. But it is more important that you are fit. And as well as looks are concerned, take professional help, learn what goes best on you and change the way you wear you makeup, hairstyle, clothing etc., If you think cosmetic surgery will help and you can afford it, go for it. Have healthy food and get regular exercise. However, do not overdo anything, because excess of everything is bad.
Ultimately, feel good about yourself. If you feel good you will look good. Most of the time you will not be able to change the way nature has made you and it is not in your hand. But, the way you carry yourself; your grooming and your personality is in your hands. People will like you not for your good looks but for your good personality.
Change your belief system
A conservative and orthodox belief system may be one of the greatest hurdles in having a positive self image. Religion is good and all through this site I have advocated the power of faith and God. However, most unfortunately there are some of the things in all religions that show human beings in poor light. I am convinced that God who loves us all can have never said it and it is all creation of a few selfish people who wanted to keep entire humanity under their clutches by injecting such self limiting belief systems.
So, it is advisable to have more liberal and flexible belief system. Decide yourself what is good for you and do not blindly follow dictates of scriptures that are mythological. Discard what ever belief you think is obstructing your internal growth and replace it with a new one. I am not saying, that become a rebel, because that is another manifestation of low self image. But simply, understand the difference between 'principles of success' and orthodox and superstitious belief systems.