A good way to start affiliate marketing is by building a long e-mail list of people who are interested on your niche. There are many methods of building a list, some are fast, some are slow, some productive and others not.
A good way is by giving away something for free (like an e-book) to people who give their name and e-mail address. This way people who are interested will give their e-mail address and you will be able to contact them in the future to promote your paid products.
Something that is good to avoid is buying an e-mail list, because you never know if the list will contain e-mails of people who like what you are promoting or if in the list there are many bots. Many people are disappointed from buying e-mail lists.
Have you tried to build an e-mail list, what methods you used? If not, are you willing to build one?