All the aforementioned tips are valuable. They are all critical for your success and in addition to some more parameters that I would include, they should be addressed in details in your international marketing plan.
Do you have an international marketing plan? A marketing plan will also outline the reasons that you've selected the USA market - a very big market with great potential but at the same time a very tough one to penetrate for foreign companies and very costly as well.
My recommendation is to prepare an international marketing plan - it will save you a lot of money, time and will assure that your sales and marketing activities are based on a sensible strategy.