Decide how you will use the garden: entertaining, children, growing, low maintenance. The layout should follow the use.
Get a written plan showing hard landscaping, lawns, planting, fencing and any clearance, so every part is priced.
Ask for a fixed price, a start date and an estimated finish, and what happens to waste and spoil.
Structure first, planting second. Borders, shrubs and new lawns go in once the hard landscaping is finished.