Adsense optimization on an established website

We need an EXPERT to optimize the Google Adsense on our website. We have had Adsense running for a couple of years now, but it has only been implemented by ourselves with no real knowledge in this area and as a result isn't earning a great deal. We therefore believe it's time to have it looked at. The main part of the website is a forum. It has a couple of content pages & a member photo gallery. It is very important that the adverts do not become a nuisance to users & are not TOO obtrusive. We average 15,000 uniques & 1,600,000 hits a month. However, we are seeing little above £20 GBP each month. Please provide details of how much, judging by the statistics given you believe you could get the site earning. Thanks.