The reason behind blushing cheeks is due to the blood vessels. These blood vessels are the actual reason which causes this natural blush on our cheeks. To acquire this natural blush you will have to think of some event which causes embarrassment or shyness. Due to this feeling your heart rate will increase and so will the flow of blood from the blood vessels, this will make your cheeks red, in other words blush.
Another way to blush is to think about something which makes you angry. The entire technique depends upon the swift flow of blood through your blood vessels. Remember you will have to fully concentrate on something that really makes you upset. Only until your mind is concentrating on this will you start to see physical changes taking place. Think about something that really upsets you and your mind will begin to react accordingly. Hopefully this technique will work to get you to blush.
Another method is by pressing your cheeks with your thumb, this will help in making your cheeks red. Be careful while pinching your cheeks because if the attempt too hard manner it will leave finger prints behind. However, if done properly you can use this method to make yourself blush or at least look like you are blushing in relatively short time.
You can also stand on your head by carefully leaning your back against a clean wall and keep a cushion on the floor for your head to rest on. By standing on your head the blood will rush to your face and hopefully make your cheeks read. Remember to do this very carefully as you do not want to fall and injure your neck or back. It might be a good idea to have a friend hold your legs while you do this for a few minutes.
Try to think of something that embarrasses you. Usually thinking about something like this will help you to start blushing. Remember this thought can be anything personal and you do not have to share it with anyone.