Tips on doing deals with UK and JP companies?

My small startup has been contacted by several companies in the UK and Japan, and we are in the process of negotiating pilots and paid deals with them.

I am based in the US and have heard that there can be noticeable cultural differences, and I want to avoid miscommunications that derail our deals.

Anyone have tips for how an American should adjust behavior/language/expectations when dealing with companies in other countries?