There are lots of ways in which plants can be used to increase privacy and to provide a screen. The selection of plants that can be used will vary greatly depending on what they are being required to provide and the space in which they are to be planted.
A smaller area may require more upright growth habit whereas a larger space could be planted with a variety of trees and shrubs some with spreading habit to go alongside the more vertical. Magnolia can be a fantastic evergreen option, along with deciduous trees such as Oak with its beautiful crowned canopy or Liquidamber giving the most incredibly autumnal colour. Shrubs possibly a lilac or a small tree like Parrotia Perisca can be planted along side these to give more cover and interest over a large proportion of the year.
If wanting complete year round privacy, an evergreen should be selected and which evergreen will then depend on the space available, ultimate height that is needed and the speed of which privacy or screening needs to be achieved. Thuja Plicata is an extremely useful and popular evergreen with a reasonable growth rate creating very dense cover, able to grow to some size if wanting a plant on its own to block a view. Practical solutions for a much smaller garden could be to train Pyracantha up trellis panels, pleach trees such a Beech, Lime or Hornbeam or pollard a colourful variety of willow, not only giving excellent summer screening above a fence or wall, these will add architectural interest. When pollarding or pleaching, these methods over time will also provide decent year round screening as the branches become denser.
The huge variety of options available to interrupt unsightly views, break up a space or divert the eye, means that, apart from the obvious of “will it grow on the proposed site” comes down to personal preference.