Looking at affiliate marketing in its most basic form you will want to work out which products and or services you want to promote.
Be it ppc or organic search engine traffic you will want to find a niche to get best results. A niche may be the product or service or it also maybe keywords that are not highly targeted that still get search for.
This option of finding niche keywords with little or no competition is one of the methods that can be used for good effect.
By using tools such as word tracker you kin research key words in any industry to work out how many competing sites there are that target those keywords along with how many times a keyword is searched for.
Now this will take some time to get working as you will need to test all the keywords you are trying to target and you will also want to be selective about which keywords you target as some may not convert. I.e. If someone is searching for free bingo are they likely to be looking for a site where they are going to deposit… not likely.
Happy hunting.