I sat 8 Nat 5's last year-Maths, English, French, Graph Comm, History, Physics, Biology and Chemistry. I managed to get 7As and a B in French (Party due to the fact my teachers were terrible and I refused to study for it
).
My advice would be to practice the specimen papers again and again and again. You will also have the papers I sat last year on hand too so you will have more revision material than I did.
For science based subjects doing questions again and again is the best way to do it, making sure you understand the concepts and can easily answer most questions. Biology is a bit different however, for bio make sure you understand and know your notes as there is no formulas or anything like that.
Make sure you have your assignments out of the way so you can focus on studying, It is damn near impossible to score high in them. Then again we were given them 2 months before our exam so maybe this year it will be more organised.
Can't comment on business as I haven't sat it, but for English just make sure you know your poems and set texts inside out so you can adapt to any question. Also remember to answer the question in you essays through topic sentences and remember your analysis!
Also can't comment on Spanish, just learn all your vocab cause that's what let me down in my French :P.
God that B really pisses me off xD.