Do not jump into BIG ONES!
Do not start big networks where many products & advertisers are there. First choose a simple & small product and which has popularity but new. I told you this because people are always going to taste new products. Write some good review about those & gain the trust of your readers.
Which one to choose & start with
First search Google with your favorite types of products such as Cheap Domains, Cheap Hosting. And there you'll will find various sponsored links. You click anyone that attracts you. And entering there you can find for Affiliate Page & sign up there. If that site so not use Affiliate Programme, then you can use another site this way & put your effort on single product. Gradually you can focus on some others joining big sites like cj.com, clickbank.com & many others.
I am using Mochahost
This is a nice place I got to earn with. You can also join here following the link here- mochahost.com/affiliate.php
Read the following books to become expert in the field of affiliate field...