Got accepted by this year's GSoC, and following are some tips for anyone who may be interested to apply:
Feel free to contact your potential mentor: mentors are all friendly and kind people, they will be glad to guide anyone who is willing to contribute to the open source world(at least in my experience), and their opinions really matter in your apply. So please pay more attention on your communication. Even you are not accepted, their help will makes your coding easier.
Pay attention to the project you want to apply: to show that you are the right person for them, you have to dig into the project and make some patches. Maybe it's not easy for a person who is totally new to a project to make a patch, but you really need one to show your programming skill and interest in that project.
There are a lot of helpful information on the Internet about GSoC, but these two tips above will make you special out of other applicants. Hope it will help you~