Without doubt join an affiliate program. No need to develop your own products - it's all been done for you. There's a great selection at ClickBank and it's easy and free to register.
Get a head start with my free book ClickBank for Newbies - which includes a money-making opportunity for both newbies AND veterans.
Put your affiliate link in ad or a traffic site and sit back and wait for your reward, which will be - nothing.
There's one absolute must that an affiliate should have, explained here
Along with ClickBank for Newbies above check out The Ultimate SuperTip