In addition to this excellent source, I'd like to add the advice of an associate who is currently growing marijuana in Canada for fun and profit.
Growing any significant amount of marijuana indoors will produce a noticeable smell that practically anyone can detect, unless your neighborhood is particularly windy. In neighborhoods with multiple grow houses, the odor can be especially strong. If you find that several nearby houses are also growing, you have a chance to grow yourself and avoid suspicion by simply blaming the smell on the neighbors when anyone asks. This works especially well if you distinguish your house, yard, and cars in a way that makes you look nice and square.
With a widespread electricity crisis in full swing, many indoor growers are resorting to electricity theft to power their grow lights. Law enforcement agencies have generally caught onto this, and may bust growers on electricity theft alone if local laws against growing marijuana aren't very strong. During winter, indoor growers can save on their heating bill, since their house can be at least partially heated by their grow lights. With enough lights, it might even be necessary to vent cold air indoors to keep the indoor temperature bearable. Because of this, it is possible to spot a high-volume grow house in winter because its windows are open and the snow is melting off the roof. In summer, many serious grow houses may not run at all, since the cost of operating a refrigeration unit all summer long for the rest of the house could be substantial.
Big-league indoor growers may not even live in the grow houses, both for reasons of comfort and the risk of arrest. Careful planning and cutting-edge hydroponics have made it possible to run remote grow houses that require very little maintenance, as little as a quick visit every two or three days to refill the equipment.
The advances in growing technology are surprising even the most seasoned indoor growers, so it pays to find a grow shop you can trust. Once my friend figured out his local grow shop owner was cool, he stopped claiming he was growing tomatoes and got the shop owner to reveal all kinds of soil and fertilizer blends optimized for marijuana. The common sense rules still apply here. Pay cash, use a safe mail drop for any ordering, and drive a car with untraceable plates when making grow shop supply runs.