I'm starting trading with bitcoins a couple of month already i buy low and sell high but really i wanna know if there are any strategies or equations to follow to know which time is perfect to buy or sell or which is not and so on ......
im looking to start trading as well, anyone wanna help me out by telling me a good exchange with low fees?
They all have pretty much the same fees. So you won't win much here. More important is that you should think about verifications. Some exchanges need you to verify even if you never send Fiat money to them. Even if you just send and withdraw bitcoins. Bitstamp will make you do this for example.
I would use btc-e if I was you. They don't make you verify your IDs just for Bitcoin trading. They are pretty sound security wise and they have great Android application if you are on the Android for trading on the go.