I've painted the backs and bottoms (and sides on one of them) of several glass tanks, and the best method is many light coats. Put on as many light coats as it takes until you can't see light through it. Use a flashlight to test this. It might look like it's dark enough after just a couple coats, but a flashlight will show you pinholes and light spots where the paint missed you would not see just by eyeballing it under normal lighting. Make sure you do very light coats to avoid running or pooling of the paint. As for cleaning the glass before painting just use some Windex or other glass cleaner, and make sure you let it dry completely, and don't leave behind any "fuzzies" from the towel/paper towel.
As for spraypainting in the house. I wouldn't recommend it, but if you must, make sure that EVERYTHING in the room is covered in some way (tarp, visqueen, lots and lots of glad plastic wrap) and that you are wearing a mask and have ventilation to the outside, that your furnace/AC is turned off, and the rest of the obvious stuff like no pets in the room, no smoking while spraypainting in a closed in area, and no open running fish tanks.
Since you are spraying it inside, make sure there are no flame sources nearby like a gas water heater, furnace, or stove. Next make sure the area is well ventilated. 3rd, clean with any window cleaner and a straight razor blade to make sure there is no film or water scale. 4th, clean with alcohol. Mask off the areas you don't want painted (sides and any trim). 1st coat should be a VERY light coat. Next coat heavier, but not enough to run or sag. I would do at least 3 coats, and after that look at it from the front to make sure it is even and you didn't miss any spots.