My site's fairly new and doing well on google.co.uk but it's no where on google.com . Is there a way to focus SEO on google.com?
Yes there is check your ranking for your keywords on Google.com seek out the competition and then develop a plan to outrank the competitors ie: more back links, more quality content, social bookmarking sites ,etc
google.com is a world wide website that normally visitors search for their convenience. google.co.uk is also google searh engine that the uk visitors mostly visit.. Depending on the geo target the optimization depends...
To improve google.com rankings you will need to indicate you are an american based website. Changing your host to an american IP and getting links from other .com sites could help.
Buy a .com domain and host it in the US. You need to decide where your target audience is and focus your efforts accordingly.