Don't assume that just because a company sells and installs solar panels means they are good and trustworthy people. Shop around. Get a minimum of three quotes. Read all contracts. Check backgrounds of potential contractors. Deal with this like any other home-improvement project that you would otherwise do.
When planning your panels, take into consideration the shadows that nearby trees may pass over the area. Solar panels usually need to be mounted high on the roof, in a location that is exposed to the sun for the longest period of time. However, what seems like a great spot may be covered in shade for a certain period of the day.
Solar panels must be cleaned regularly. If your home is in a filthy region or close to the desert, they should be hosed weekly. Regardless of air born dirt and dust, you should do a through cleaning every couple months. Clean solar panels are productive solar panels.
Make sure that any solar panels you put up are actually cost effective. While the installation cost can be dented with government assistance, you need to know how long it will take for energy savings to return your investment. Also factor in that you are not likely to get the same amount of power every single month.