Focus on reviewing products that fall within your niche. Then, leveraging the rapport you have created with your audience and your stance as an expert, tell your readers why they would benefit from purchasing the product you are promoting. It is especially effective to compare this product to others in the same category. Most importantly, make sure you are generating detailed, articulate content to improve conversions.
Many affiliate programs will often run promotions with good discounts or giveaways that might be attractive to your audience. For example, if you're an Amazon Associate and the site have a big Holiday Sale, it would be the perfect opportunity for you to promote discounts to your website visitors. This is a great way to promote your offers while also providing good value to your audience.