Use Low VOC Paint where possible. These create less fumes than traditional paint, but can cost a tad bit more.
Ventilate the room well to remove any excess fumes. Window or box fans work great for this.
Cover the top of the tank if it is an open top or open canopy. Turn off the skimmer if painting in the immediate vicinity. Put some carbon in a bag in the sump just in case the fumes enter the water somehow.
Most importantly, ventilate the room well... Read the warnings and if it says harmful to pets, I would look at a different paint or seal off that room the best you can from the tank. Painter's tape and drop cloth does wonders if you need to seal off your tank temporarily. I did that when the exterminator came over and sprayed and the tank was fine.