When I started my garden, I began with our site plan. If you bought your property, you should have a copy of this somewhere. It's the 'map' that shows the shape and size of your property, the location of your house and any permanent features (like driveways) as well as any easements or rights of way that go across your land.
Easements and rights of way are important because you don't want to plant anything on them than can't be moved easily, if need be, and it is unlikely that you would be permitted to build anything of a permanent nature on them.
Your site plan might also show, if it is more than a simple plot plan, the contours of your land. Contours are indicated by lines with numbers which show (usually) the elevation of the ground from sea level, or by numbers alone, which indicate 'spot' elevations. Most site plans are drawn to an engineering scale with one inch equaling so many feet, generally 20, 50, 100 or 200. Since I'm used to working with plans to scale, I find knowing the scale of a drawing important to me. It is not absolutely vital to work 'to scale' in order to determine the major elements in your garden. You can plan flow without scale. Being able to draw in scale really only becomes important when trying to work out details.
If you don't have a site or plot plan, you will need to make a rough sketch of your land and place any existing permanent structures on it as best you can. You can guess them in or pace them off if you don't have a 50' or 100' tape measure. You do want to try to be as accurate as you can because it will save you time and effort in the end.
Note on your plan the four points of the compass as nearly as you can determine them. Locate any major trees, shrubs and other features you are unlikely to want to change. Note the spots that get dry or stay wet; the places that are sunniest or shadiest and the direction your prevailing winds and storms come from.
