Withdrawal is not a safe method of contraception unfortunately.
You should definitely use a "proper" method such as condoms or go on the pill, unless you want to run the risk of getting pregnant, or even catching a sexually transmitted disease!
As you probably know, guys get something called pre-ejaculatory fluid which is the clear substance found when a guy is aroused, but before he has ejaculated.
People of certain religions use withdrawal, as contraception is banned according to their beliefs... but you will find that there is also a higher birth rate for these people in general, so it really should not be used unless religion is a deciding factor for you.
There are many methods of contraception that you could try.