When deciding which keywords you want to promote in your search optimisation campaign - try to think about it from the users' point of view.
A mistake that many companies often make is to pick keywords that they use in their industry, but their customers call something else. For instance, in the print industry, the term 'Back Up' means to print on the reverse side of something - but to most people, the term 'Back Up' means something completely different.
It's usually worth picking specific keywords where SEO is concerned. Often, generic terms can have multiple meanings, and Google may not associate it the way you think. An example might be a builder, wanting to promote their services doing rendering on the outside of buildings. If you search just 'rendering' in Google, you will get results on a number of subjects (3D graphic design, animal waste, etc.) - but a search for 'External wall rendering' will yield much more targetted results.
In addition - a more targetted keyword will often attract a 'warmer' customer - if someone is specifically searching for your product or service, they are more likely to buy.
If you are offering a specific service, it's often advisable to choose keywords that indicate the user is looking to buy something. For instance, if you offered 'cheap holidays in Spain' - that exact phrase might be a good selection. Note the buying term - 'cheap', indicating the customer is interested in the price. Another example could be 'gas boiler installation' - the key phrase in this case being 'installation' - they want something done.