With affiliate marketing, you have no control over the product you are promoting. You cannot control the look, description, pricing, or the after-sale service of the product. This does not suit everyone. This can limit what you can do as an affiliate marketer from an advertising point of view. You may not be able to mention certain features due to your terms and conditions. If you do not personally receive the product you may rely on photos. These may be outdated or of low-quality, making it hard to promote the product effectively.
Creating blog content is a very useful and effective way of consistently building content on a site. When creating blog posts, it's a good idea to do some keyword research to figure out what it is that your audience is interested in and searching for online. Also, be sure to research competitors, forums and social media to narrow down on topics for your blog. 
Will my target audience realistically spend this amount for the product? Again, your reputation is on the line here. Is the product you are thinking of promoting priced reasonably for your audience? When I was writing my ebook, I was stuck on pricing. I asked around for opinions. A number of people suggested I price my ebook at $47! Their idea was to price according to value, not size. In my mind that was crazy. My network was composed of a lot of stay-at-home bloggers, and my collective audience was comprised mostly of people without a whole lot of disposable income. There was no way anyone was going to pay $47 for my 30-page ebook.
There is serious competition in the affiliate marketing sphere. You’ll want to make sure you stay on top of any new trends to ensure you remain competitive. Additionally, you’ll likely be able to benefit from at least a few of the new marketing techniques that are constantly being created. Be sure you’re keeping up to date on all these new strategies to guarantee that your conversion rates, and therefore revenue, will be as high as possible.
I personally prefer to do it that way--you can create a more convincing review that's more likely to make sales. It's not always possible or practical, though; for example, would you break up with your significant other just to test a product for getting your ex back? ;-) In cases like that, or if the product is expensive, it's usually best just to use the vendor's affiliate resources instead.
Watch them. How are other content creators in your niche utilizing advertising? What types of ads do they use? What are they promoting? What do they talk about repeatedly (if you keep seeing the same affiliate product show up again and again, there’s a good chance they’re making good money from it)? If you see a product or service they talk about that jogs your memory and you can ethically promote it too, find affiliate information by the methods described above.