I think it was Don who'd asked about this a couple weeks ago...at any rate:
A shallow pond, or a pond with shallow areas, especially, a gentle slope to about 2' in depth. NO FISH - they'll eat all the nymphs, so you'll never get an established population. Rocks on bottom, creating nooks and crannies. A few different types of water plants with roots at various levels (hiding places for the nymphs), also having various heights (above water). In a small pond (i.e., half-barrel or similar size), yu can still have a water lily, and a couple different sedges/rushes. When the nymphs are mature, they climb up the water plants to emerge from the nymph body and to dry their wings. Then, the adult dragonflies like to use tall rushes as perches and "watchtowers". A dragonfly can spot a mosquito up to a distance of 40 yards.
The pond will also attract mosquitoes, however, the dragonfy (and demselfly) nymphs are ravenous and aggressive predators, so you might not get any mosquitoes actually hatch from the pond. ALso, a pump that keeps the water very gently agitated will disgourage many mosquitoes - but you need some larvae to feed the nymphs.
HTH