While good SEO skills will get your page noticed by search engines by themselves there other tricks to help increase their effectiveness. Affiliate programs can be a good way to increase your websites own SEO attributes. There are different types of affiliate programs. An older one would be the old banner concept which predates pay-per-click. Googles Adwords is a modern incarnation of this where by people can profit from Googles pay-per-click business. Lets look at some of these.
Not all affiliate programs have to be for profit. There are many people who are just looking to get traffic to their sites by cooperating with other sites. Just as a strong page on your website can help increase the rankings of your other pages rankings on affiliates sites can do the same. Dont confuse affiliates with guest books or link pages. An affiliate is working with some kind of service or business to make a profit so it is a function of commerce. This will help with the search engines rankings. Search engines look for link pages and dont give them a very high ranking so they wouldnt help you very much. However since affiliate pages are used for commerce they are going to have a much stronger ranking. Affiliates can act as a team just like the pages on your site.
Another point to consider is that pages that are involved with affiliate programs are going to be set up well in order to profit from them. So this is analogous to strong members of a team making a colossal team effort. Enough strong pages driving traffic to your site is lie diverting a river to a drought stricken town.
Fortunately affiliate programs are easy to find so just keep in mind what kind you would be willing to do for your site. Dont give yourself more work than you need to.