How tall the fence is to be is obviously a requirement as is the length, location of corners, and gates. It is wise to have someone stand on the proposed fence line with a tape measure while the site is being observed by someone else from the most important viewing locations. This may reveal that the height that looks right when standing on the fence line does not produce the desired screening or atheistic line when viewed from the most important vantage point. You should consider the two sides of the fence. Single sided fences of some styles are often less expensive that double sided fences.
Some fences can slope to grade.
Many cannot and must be stepped down a slope. The amount of slope effects how the panels should be sized and in some cases actually manufactured. When making a plot plan of the fence line, showing gates, and corners, include the slope. This can be done with an inexpensive string level available in hardware stores, a piece of string, two people and a tape measure. Have one person hold the string at ground level and pull the string out about ten feet.