Here is a thread that discuses some affiliate marketing tips. Feel free to add some tips.

Do your research- Keep your eyes open and choose products that people will want to buy. Check out what are the most common brand names that appear everywhere.

Use a combination of texts and banners for your advertising campaign- Donít make your website too intrusive or flashy, because, if you overuse them, they will clutter your pages and tick people off. Use well appointed banners and try to make them appealing to everyone.

Make sure that you read carefully the "Partner Agreement" and terms before committing to any affiliate program- Compensation rules and overall regulations are important because they can determine your marketing campaign and prospects. Some companies have really strict rules and prohibit the use of particular brand names or logos and trademarks. Companies, sometimes, supply the affiliate marketer with already approved content that can be used in promotional campaigns.

Pick products that can be found only online This increases your chances to sell them and attract a greater number of visitors and customers. Try to incorporate coupons, free deals or other offers; they will attract customers and they are always effective and catchy.

Do not expect a huge flood of income right away- Give yourself and your affiliate program some time and just try to place the ads and banners on your blog accordingly, until you find the most appropriate and effective mix. You have to keep experimenting. And remember to keep your patience.