Outside, you need access to water (usually just a hose, unless you set-up a float box system), an electrical box (preferably with a switch) and a flat surface on which to place the base. 

Think about where you will see and hear it the best.  Putting a fountain under a tree may look nice, but it also guarantees you will have to clean it more frequently.  Tucked into other planting can work nicely, but don't forget to leave yourself room to get in and clean it, and be sure it complements the rest of your landscaping and is appropriately sized for the area. You don't want your nice new fountain to "get "lost" or "take over" your entire yard.

If your base does not have a drain, please follow the instructions for indoor fountains.  

If your base has a drain with a threaded plug and handle on it, the best installation will have a 1 1/ 2" pvc pipe buried directly beneath the drain outlet which carries the water away quickly when the plug is opened.  If your site has a natural slope, the pipe can be buried along the slope's contour.  If the site is flat , the best solution is to make a berm at least 6" above the surrounding grade to create a slope for the pipe.  If necessary, you can dig a pit under the base that's large enough to accommodate the water in the base and a rinse and drain directly into that.

Smooth out the base area, removing anything that could damage the base.  Make the area nice and flat, with a very slight sloping towards the drain area.  

Dig out a slight hollow to accommodate the circular drain area in the pan and  set a 90 degree pvc elbow just below ground level . 

Attach your drain pipe at that angle so the water will flow down rapidly.  

Place the base. Place the pump in the base and thread the pump cord through the pump cord tube so it can be buried.