As with anything, safety comes first. When you have a glass box filled with water and include various electrical appliances connected to it, you can see there is the potential for disaster. Here are some tips on making your fishtank safe for both your fish and your family.
Tank placement is very important.
Do not place the tank on a piece of furniture not specifically built for holding a fishtank. Water is very heavy, for instance... a 10 gallon tank filled with water and decorations can weigh over 100 pounds! Also, do not place the tank on the floor where it could be kicked or tripped over.
Make the tank as level as possible.
With all that weight of the water pushing against the glass sides of the tank, you really don't want anything to weaken the tank and compromise its integrity. One of the main things is to make sure the surface the tank is resting on is flat and regular. If there is a small bump or irregularity on the surface it could stress one portion of your tank where it may crack.
Tether the tank to the wall if necessary.
If your tank height is large (18"+) or on a stand which is fairly tall then it would be a good idea if the tank was tethered to one or two studs in the wall. This would make the tank much more sturdy and less prone to tipping in the wrong direction. Tethering is especially important if it is in a high traffic area or if there are climbing monkeys in the house.
Loop the power cords.
If you have a fishtank on a typical stand, it is about two feet above the usual placement of an electrical outlet. It is important that the outlet is not along the lowest track of the power cord. There should be a dip in the cord which is lower than the outlet. This will prevent water from dripping into the electrical outlet, which would be very bad news! << picture here >>
Use a Ground Fault Circuit Interruptor (GFCI).
If your outlet does not have a GFCI built in, then you should purchase a power strip which does use one. The surge protector ensures that if an electrical current should enter the tank (either from a frayed wire, sunken light strip, or broken heater) that the circuit will immediately be broken, saving you and your fish from a powerful repetitive shock.
Turn off all electrical appliances when servicing the tank.
As mentioned earlier, water and electricity is a dangerous thing when combined together. To prevent any electrical shock to you or your fish, always turn off ALL of the electric appliances that are connected to your fish tank when you are servicing it (water changes, algae scraping, etc.)
Use a cover adequate for the aquarium.
There are many reasons to put a cover over your tank. One reason is to prevent some fish from jumping out (many fish do this regularly). Another reason is to keep foreign objects out of the tank. Objects such as cat paws come to mind, but also children's hands can be just as bad for the fish. Especially when they have a fistful of cheerios to "feed the fish" with...
Put the fish food and medicine in a safe place.
There are a lot of products on the market which are indended for aquarium use only. Fish foods, medicines, chemical test kits, and other such products need to be stored in a safe place. Brightly colored bottles with screw-tops will definitely be found interesting to children or sneaky pets, and that must be avoided.
Wash hands before and after servicing the tank.
There are many living organisms in your tank other than your precious fish. This is to protect you and your fish. Various bacteria, algae spores, nematodes (worms), even single-celled organisms such as paramecia are moving about in the tank. It is extremely rare that anything would be transmitted to a human, but it is still a very good idea to prevent any potential risks by scrubbing your hands/arms with unscented soap prior to and after servicing your tank. Make sure your hands are devoid of any soap residue before putting them in the tank.