Start by listing out what has topical relevance to your blog. That matters more than what programs are best.
Then seek out products in your niche and consider the main 3 routes you can take.
- Amazon Associates - To reach a wide range of products on the plus side but low commissions and cookie periods.
- Affiliate networks - These networks allow you to connect with lots of products, vendors etc under one account. This helps you hit the payment threshold more easily and often offers much higher commissions and longer cookie periods than Amazon.
- Direct affiliate programs - Seeking out the websites of brands you want to partner with and Ctrl or Command + F to find the word “affiliates” or “referral” in their footer. Then sign up direct or find the affiliate network they use.
- Use Google, Product name + Affiliate programs to find list articles and sites that contain the terms you are searching for to bypass the hard work.
Realistically if you are a blogger you could be writing about any subject under the sun.