Measure the area where the gate will be installed, or decide how wide and high the gate will be, if the posts are not yet installed. Typical gates are between 24 and 48 inches wide and 36 to 96 inches tall. This will mostly depend on the style of fence that you will be installing.
Draw the posts and slope of the land between them on a piece of graph paper working in a 1:12 scale, which means that 1 inch of drawing space will represent 12 inches in the real world. Use a scale ruler, which automatically translates your measurement to the correct dimensions for your drawing as a straight edge and ruler, so that they are crisp and clean. Use the edge of the ruler labeled 1:12. Avoid adding shading or other marks that might cloud the lines.
Copy the drawing of the posts and ground beneath, by either drawing a second copy or using a printer or copy machine. Draw the gate from both front and rear views as it hangs on the posts onto the same paper with the post and ground drawings.
Draw the horizontal rails, diagonal braces, latches and nuts on the hinge bolts on the rear elevation, or drawing. Diagonal braces should run from the bottom of the hinge up toward the top of the latch side to provide lift, if you are using them. Make notes on the drawing regarding the type of materials, hardware and fasteners you want your gate built of. Include model numbers and brands when possible, especially if you will not build the gate yourself.
Diagram picket spacing, style and size on the front view. Draw in the hinges, including bolt placement. Study the ground where your gate will be hung to determine how the bottom edge of your gate needs to be constructed. If the gate opens on fairly level ground, or the slope is toward the latch side, choose the highest point of the ground and draw your gate ¾ inch above that point, straight across from side to side. If the gate will be swinging up hill, determine how much and draw the bottom of the gate angling up from the hinge side to the gate side, to accommodate this, so that the gate will not hit the ground.