[Bodhost]

The best way to assess what are the right keywords to use is by using the Google Adword Keyword Tool.
Start by brainstorming a selection of words you feel people would be likely to type to find your business.
Think about your industry and decide if your target market is a local one or national market.
If your business is an ecommerce shop or you offer your services across your country then a national phrase is best but if you are offering services to the local community i.e. Roofing London then a local phrase would be better.
Type your phrases into the keyword tool not forgetting to add London if its a local target market as demonstrated below. (use London in your search even if this isn�t your area as it gives more accurate results).