The reason why people search on the web is to get a solution to issue or need. Either they need a specific something, by name, or they know they need something, but are not sure what. Make sure your website sufficiently addresses these two audiences.
The most important thing your website can do is help solve a prospective customer's current problem.
Why are the most popular websites on the Internet search engines? Because they help someone do something. Sometimes it's just to learn something about a topic. Sometimes it's to find something to solve a specific need/want/desire.
Does your website help your prospective (or better, current) customers solve any need, be it informational or transactive?
Unless you sell or deal with specific name brands that customers are looking for, you should focus your website's content on the most popular usages for what you sell or provide. What are the different needs it serves? Do you focus in specific industries?
The first place to start is to with your customer. Build a profile of who your customer is, or who you want them to be and what you want them to do. Give your profile a name. Think of your profile's need for information. What do they need to know in order for them to reach the conclusion you want (do business with you), to your mutual benefit (their needs are satisfied (at the least)).
Again, turn back to your current customer base. What are the questions you answer in order to move the sale forward? Have you documented them or just committed them to memory so you can rattle them off on the phone or in person? If you have everything "up there" you need to write it out on your website, "down here." Because that's what most of your website should do. Answer ALL the questions. Make some up if you want to. Make sure they are chock-full of the keywords and phrases you want to be found under. If you serve a specific geographic region, make sure you include that as often as possible.
What keywords or phases should you pepper your content with? Well, the ones that you see in your website traffic logs and if you have a site-specific search tool, hopefully you log searches. As well as the ones you want associated with your company/product/services. But you cannot just stuff them in there. You need to work it in where appropriate. If it's excessively overdone, then even if it ranks well, it may turn people off. And that's not the result you want.
Until Google can search your brain, just because YOU know something someone else needs to know, they have no way to know, unless you post it to your website. The great thing is that, unless something changes about the information you published, you will be able to refer customers and prospects to the information for years to come (in newsletters, direct email, on the phone, etc).
Of course, the biggest benefit to come from this is that hopefully your page will be found by someone who can do business with you, but didn't know you existed, but does now. And now considers you to solve their problem. What is better than that? New, fresh and free prospects. Make sure you have strong call-to-actions on your website and in your content, about what you want your prospect to do, such as Add to Cart, Email Us, Call Us, etc. This way you can clearly guide them to what you want them to do next. Hopefully they will.