One of the most sought after and highly recommended course is this one on Guide to Effective Affiliate Marketing Strategies by Kudus Adu. Not only does he focus on create an affiliate marketing strategy, he focuses on best practices to create money pages, tells you how to build your email marketing list and how to profit from it. He clearly asks people looking for ‘get rich quick strategies’ to stay away from the course. More details here.
The products and services you will be promoting to your audience must be relevant and good quality. Make sure you believe in them and know everything about them, because this will be crucial to you delivering the sales pitch to your audience. You need to build trust with your audience so make sure the products and services you choose to promote are trustworthy enough.
When promoting affiliate offers, just make sure you are fully aware of all the terms and conditions attached to your affiliate program. Some programs can be strict about how they allow you to promote their products. For example, some may limit you to banner ads and links only, while others will allow you to use paid advertising, but won't allow email marketing.