Hi,
The prices for your flights depend really on the destination within the USA. For places like New York, the prices are always cheaper because of the high frequency of flights, but for the others the prices are higher. Sorry, but in July every destination in the USA wil be more expensive to reach because its summer holidays. If you could be more flexible and change to August the prices come down dramatically. An example. 27th August - 1st September to New York. Continental Airlines Heathrow to New York, £275pp rtn, a bargain. Try wefly for flights its always cheaper than going directly to an airline, even during July.
For other places you are best just to keep checking for any cheaper fares however, its doubtful for July, sorry. Sales are usually during the not so busy months so i think you will lucky to find a cheap ticket in July
With regards,
Luke