Hi Steven,
Maybe my view on this matter can help you a little.
First of all you need to analyse the playing field. So use a tool like ubersuggest.org to get all the relevant search queries and variations for your type of business. Check also some Google suggestions at the bottom of the search result page for some good / popular variations.
After you determined all the relevant keywords (including long tail keywords) for your business you can insert them into Google Adwords keyword planner. The output will give you the expected monthly search volume and, very important, the level of competition on a specific keyword.
Based on your domain and page authority compared to the top ranking competitors you can asses whether its possible to get some top rankings on high volume search queries. When the competition is modest, and comparable to the authority of your website, you can challenge them by creating some high quality landing pages. However if you find competitors to have more authority you can decide to try to rank for keywords with a lower level of competition.
If the difference between your site and the top competitors is not gigantic, I would try both. So try to rank between the big boys and go for the long tail search queries. Bear in mind it's all about the visitor. If your visitor finds your landing page useful, then the chances of a good / better ranking will improve. So try to write the page with the customer in mind, make it very relevant. But if your competitors have a lot more authority, I would start with long tail keywords.
It is possible to rank for "dell computers" if you try to rank for "Dell Small Business Computers". However if your competitor has a very relevant page on "Dell computers" he would probably rank higher.
Of course you'll need to analyse the performance of your pages with MOZ 
In order to make the necessary changes and improvements.
Good luck!
Kind regards,
Herman (from the Netherlands)
