I'm going to guess you're at GCSE level? The three sciences are generally a lot different to revise.
Biology: You've got a looooad of facts to remember here, so memory aids like flash cards, trying to remember in 'chunks' (for example, instead of trying to learn everything about disease, try to remember what pathogens/antibodies do, what white/red blood cells do, etc.) Because even if you don't remember everything, you'll still remember
something!
Chemistry: Practise questions are the best way to go for this one! A lot of questions will be testing your knowledge of how to work stuff out, so you just need to make sure you know how to balance equations, work out molar masses etc (depending what level you're at). A quick google/wikipedia of Group 2 and Group 7 elements really helps too for stuff like Electronic Configuration and reactions etc.
Physics: It's been about 6 years since I did GCSEs so I don't know if you still get given formulae in the exam, but it's a good idea to know what they are and do some practise on algebra/rearranging equations since a lot of questions focus on that! Like Biology I recommend flashcards for things like how forces work and which formula is used for what - also Electronics is a topic they like to ask about a lot so do pay some attention there, by practise questions.
And finally, I'm a first year Biomedical Science student so feel free to send a PM if you want help!