What criteria should I look at when I choose a product? More precisely, what do the numbers next to "gravitation" mean? On what should I spend most attention?
gravitation = gravity which is basically the number of affiliates who are successfully selling that product. Gravity does not really mean that much when you are looking for a product to promote. I would advise you to go into a niche that interests you and one you already know abit about. Its all about testing and researching when you are looking to choose a product on clickbank.
It helps to look at the sales page primarily - ask yourself if you would consider buying it after you have read the page. Any decent product will have its own affiliate pages offering guidance, bannes etc. Also make sure they only have clickbank as a payment processor - ive seen some offering paypal and others on the same page which means you lose on the commission if a sale is made through them.