I would start by looking for a really dedicated, knowledgeable breeding mentor, as Sarah says. If you are planning to breed the dog(s) you already have, their breeder may be the place to start. Otherwise someone who is breeding the kind of puppy you want for your foundation bitch. It is possible to do it without that sort of help, but you will be saved a lot of time, worry and potential heartbreak if you have the right someone to help you.
The second thing I would advise is to build up a really solid financial cushion, especially if you plan to breed toys. It is an expensive business, with absolutely no guarantees of ever covering your costs (equipment, house alterations, genetic tests, fertility tests, stud fees, pregnancy tests, scans), and if your bitch needs an emergency caesarean to deliver dead or dying puppies at 3am on a Sunday morning (and yes, it does happen!) the last thing you need to be worrying about is how you will pay for it.
To sit with a dog on a hillside on a glorious afternoon is to be back in Eden,
where doing nothing was not boring- it was peace.
~ Milan Kundera