Advertisement has a big role in providing traffic to a site but it is very expensive to buy ad clicks if it is not profitable but in the case if it is profitable then only there occurs the real use of the ad click. The real use of the ad click is needed when an affiliate promote a product because an ad click may only cost about 0.03$ or 0.06$ but if the promoted product is sold with a commision rate of 21$ then just imagine how much one can earn with the help of a small amount. The best ads to promote affiliating product is the text ads because in text ads the advertiser can provide the complete detail about the product in the text space. So that the customers only came after seeing the whole details unless your money will loss only for advertisements. CPC banner ads are also good for advertisements but the thing the advertisers need to provide in the first look itself the visitors need to understand whole details about the products including discounts and price. The best thing that an affiliate required is the right choice to pick a product for promoting. For eg most of the internet users are interested in using new apps and softwares there are plenty of specials apps are promoting by the marketing sites.
So picking a less expensive and useful software will be a good choice for promoting. In the ads itself the advertiser need to provide the payment mode to buy the product so that the visitor may understand the way they can buy the product. Don't expect that you will get 100 customers with 100 ad click only expect 2 or 3 customers from 100 clicks. So use advertisements to promote product because it is the best and easy to earn income by selling products. All the best.