Work hard from the start, resits mess everything up.
Even on modules that are easy revise lots. I got 76/100 on c1 maths due to the fact it was relatively easy so i didnt revise. I then went and got low a's on the rest of the modules and another 76 on core 3 and missed an a by a couple of marks, would have got an a if i revised properly for c1.
Work hard at coursework. Exams are easy to mess up, even if it is just a few marks lower than you expected. Good coursework could mean a lot, work hard to get every last mark, don't just settle for the grade you want at the end of the year, it is the only time that you can get some help from your teacher and others make use of this.
English lit - people seem to find this subject really tough. I have always found essay writing really easy which i guess gives you more time for planning, and coming up with good quotes etc. I think my advice would be just to do every piece of homework that you are set to the best of your ability. Writing lots of good quality essays improves your writing style and if you include lots of quotes you will remember them for the exam. Also i would advise when revising for the final a2 exams not trying to remember every line in the book, you need a lot of quotes but pick ones that fit well with certain themes and characters, perhaps some that fit with more than one theme and character so rather than remembering say three you only need that one.
And just generally during your a levels get involved in stuff going on around your college, everything you do can help with your personal statement if you are thinking of uni. And it will help with your confidence if you are a little shy.