For most uses one should take a pragmatic view of where equipment is to be located. Bear in mind that you will be taking readings for your location warts and all and not a open space somewhere else. Very often your location will be affected by the local urban, commercial, geographic and vegetation topography.

Your temperature and humidity sensors are best located in a shaded environment out of direct sunlight and weather. Here you have a lot of options. The north facing side of a wall or fence is good but bear in mind radiated heat from an occupied building. Inside a purpose made screen or even a home made one such as a white ice cream tub with ventilation holes. Force ventilating the screen will improve accuracy and response. If you have to mount it on a sunny aspect then shade it behind something e.g. a shiny biscuit tin lid painted black on the reverse.

Anemometers and wind vanes are ideally placed as high as you can mount them away from surrounding features and vegetation to ensure a clear air flow. Of course a 10m pole in the middle of an open field would be good but not many people have that opportunity. Those with the space could use a 25ft scaffold pole concreted into the ground. Otherwise any pole or post clear of obstruction would be good. Often a fence post or aerial pole will work well. If you are going to mount it on a building or chimney try to get it as clear of the building as possible to help negate the venturi effect of the building. Try to locate it on the prevailing side, usually SW in the UK. Do not put it immediately on top of a large blank wall as during strong winds the rising air will have a marked affect on readings.

The standard accepted exposure of a rain gauge is at a height of c.30cm above level grass surface and away from any obstructions. However it is more important that they are not in the lee of a feature or vegetation. Often a flat roof is a suitable place but they should always be set level on a flat surface.