For science, your best bet would probably be freesciencelessons.co.uk. Short, easy to understand videos which you then can make notes/revision
Business studies, learn your key terms and definitions, figure out the best ways to structure your answers, memorise your equations and keep practicing them. Short flash cards are best for things like advantages/disadvantages and possible points. Keep practicing exam questions, with business there's only really a limited number of questions that could possibly come up so make sure you've covered everything on the syllabus and you'll be fine.
Maths is all practice, practice, practice. Maybe find youtube videos to explain concepts you struggle to understand.