Get to know the site: where the sun rises and sets, where the weather comes from, the views, the setting - what is it you really love about it?
Rather than determine a layout yourself, think about what you want in terms of activities, the number of people to be accommodated, the way you like to live and then allow your architect the chance to work out the best way of expressing that.
Be open to new ideas, new ways of seeing. Don’t settle for something you could buy on a housing estate; your new home should be as individual as you are.