In order to get noticed by popular kids, do something that would put you in positive spotlight. Get good grades in tests, win awards, become really good in whatever sports you play, etc. If you are a computer whiz, offer to help with the school website and add your personal touches to it to make it really appealing. You can also become a member of a club, or work with charity, etc. Popular kids are bound to respect you if they see you busy doing something productive and may even come forward to help you out.
Pay attention to your personal hygiene, clothes and hair. Remember to take a shower every morning and also after gym class. Wash your hair with shampoo and conditioner, preferably one that has a good smell. Always wear nice and clean clothes to school. Try to remain up-to-date with the latest fashion, though do not wear something that you do not feel comfortable in. Wear a cologne/perfume if possible.
Do not force yourself on the popular kids. They are bound to find you weird and annoying if you push them for friendship. If they are interested in you, they will show it on their own. If not, divert your effects to become friends with people who like you.
Be confidence and have a good self-esteem. Remember to have the utmost respect for yourself and stand up for what you believe in. Have faith in yourself. However, do not end up becoming arrogant and conceited.
Try to become friends with one of the popular kids. You will find plenty of opportunities to become friends with this kid if you both are in the same class, or you both play the same sport, etc. You can gradually approach the rest of them when the popular kid you are friends with is with them in a group.
Remember to play it cool while trying to get noticed by the popular kids. Do not become over-excited when they invite you for something. Learn to say no to them every once in a while.