Two of the easiest ways to start generating traffic for your website, building your opt-in list and your credibility is by writing articles and participating in related forums.
Writing and distributing well-written articles will allow you to establish credibility with your readers and pre-sell your wares. Participating in forums related to your interests will aid you in developing products or services your fellow forum members might be interested in buying.
Understand that people aren't going to buy something from you based on your recommendation alone if they don't know you. So when you've gotten a few articles under your belt and participated in helping people solve problems in forums related to your topic of interest, then expect to receive traffic for your website, subscribers to your opt-in list and sales.
When your traffic and opt-in list begins to grow from writing and distributing articles and participating in related forums, your next step is to find products or services that people want and need. Make sure that you choose products and services based upon your new found information from the forums and from that you've gathered from your existing opt-in list of subscribers.
Again, never choose products or services to sell based on what you think your subscribers might like or profit potential. Instead, choose products and services based on research gathered in forums and responses to your distributed articles.