A fence is mostly about the posts: set them straight, plumb, and deep, and the rest follows. Rushing the posts is why fences lean and sag a few seasons later.
Check lines and rules first
Confirm your property line — building on a neighbour's land causes expensive disputes — and check local bylaws for height limits and setbacks, plus whether a permit is needed. Call before you dig to locate underground utilities.
Set the posts
Space posts evenly (commonly 6 to 8 feet apart), dig holes below the frost line so they don't heave, and set posts in concrete, checking each for plumb. Let the concrete cure before hanging rails and panels.
Build level and consistent
Run a string line to keep the fence straight and the top level (or evenly stepped on a slope). Use exterior-rated fasteners and pressure-treated or naturally rot-resistant wood for posts in contact with soil.