This has been discussed at great length, many times already. Please have a look for past threads on the subject, and have a read of what has already been said. If you've then got any specific questions, feel free to come back and start a new thread.
Any posts I write in Arial are on my mobile phone, so please excuse typos etc. Any posts I write in Verdana are on a PC, so feel free to berate me mercilessly for any mistakes