An affiliate is someone who promotes products usually via the Internet, or through traditional marketing methods. There are a vast number of opportunities on offer, so new affiliates are often bewildered by choice, and can waste time and money pursuing the wrong programs. Here are the basic problems to avoid:
Do not sell the same stuff everyone else sells - reason, the cost of advertising will be prohibitive, since Google sells advertising space through their Adwords program by the auction method - the more people who bid per search term, the more expensive that search term becomes.
Sell products that provide generous commission, man and women cannot live on peanuts alone.
Sell niche products, products with few competitors.
Choose a program that offers marketing support, FREE websites like this one SAMPLE
Do not choose affiliate programs that cheat you out of commission by having a cookie expiry date - if you get a sales lead that results in a sale, you should get paid, no matter how long the sales process took.
For maximum income, choose an affiliate program that offers second tier opportunities, and choose one that places no limit on how much you can earn.