Can some please help me? I have a friend which thinks she is the best of all. She would always try to ask me some questions about studying effectively, which didn't bother for the past few months until now. How can I help her?

It sounds like you're frustrated with her but don't want to be rude. And that's okay. If you're not comfortable with answering all her questions you can politely tell her that you're busy or that she could ask someone else for help. On the other hand maybe under her image as being 'the best at everything' is something else. Maybe she really wants to learn or she is afraid of not being good at something and in fact she appreciates your help.