You mentioned: "many times clients have already done this work. Ask them for copies of their market research reports when you start a project. It will save you a ton of time and effort!" We do this with most of our clients, like you said we have found that around 75% of the have some kind of Market research done, that saves you a lot of time and helps setting up the right SEO Strategy.
After you have identified your target keywords, you need to create a page targeting that keyword. This is known as SEO content. In many cases, it makes sense to publish a blog post targeting keywords. However, you need to make decisions based on the search intent. If your target keyword phrase is “buy black Nike shoes”, then it doesn’t make sense to create a long-form piece of content.
Product images. If you think images don't play a role, think again. When many consumers search for products in the search engines, not only are they looking at the "Web" results, but they're also looking at the "images" results. If you have quality images of that product on your site -- and the files' names contain relevant keywords -- these images will rank well in search engines. This avenue will drive a lot of traffic to your site, as potential customers will click on that image to find your store.