What structural elements - of trees and hedges, boundaries and height.  Which walls and fences paths, patios, ponds would we like.  Do we want a more naturalistic garden overall - with less ongoing maintenance - or more managed.

Work out where specimen trees and hedges should go early.  Give plants plenty of space to grow.  The detail of planting can be filled in over time.  Local garden centres will stock many of the plants which do well locally.  They are a mine of useful information.

Take inspiration and learn from what does well in local gardens.  Learn from books and take advice on where to plant and what type of plant does well for your site.  Learn the way the wind blows and the way the sun falls at different times of year.  Your own plot will have a micro-climate of its own.  And different plants will do well in different places. 

Above all enjoy the process - gardens grow with their owners in a symbiotic relationship - the garden should show something of our own unique passions.  Enjoy your creation.