GCSE MathsWatch this thread
The GCSE Maths Tutor has a 2 hour one which covers everything, I'd recommend it
Revise just a few of the topics you know are coming up (they are listed in the advance information). TheGCSEMathsTutor stuff on youtube mentioned by jessicalouisemay would be good for last minute tips.
Concentrate on doing the best possible job on the first few questions in the paper, you don't need many marks to pass with grade 4. It's impossible to be certain but something like 15-18 marks from each paper.
Double check all of your calculations. Even if you are not sure if it answers the question do everything you can possibly do with the information given in each question. Write down everything you think of and you may pick up some method marks even if you don't get to a final answer.
Don't forget you have 2 calculator papers to get marks from in June so if Paper 1 doesn't go well you have several weeks to get better ready for those exams