Many adventurers like to thoroughly explore the beginning levels, reliably gaining enough experience to successfully tackle the next level. A temple diver takes a different path.
A temple diver intends to worship a particular god, and wants to gain piety with that god as quickly as possible. The temple diver takes each stairs down as soon as they find them, in search of the Ecumenical Temple. After taking service with their god of choice, the temple diver returns to the first level of the dungeon, and proceeds more methodically, gaining experience and piety.
Temple diving gains piety more quickly than the usual strategy, as a lowly rat on dungeon level one generally gives as much piety as a dragon or tier one demon. This approach is particularly useful if the chosen god gives abilities or rewards at early levels. Sif Muna's Channel energy and Okawaru's Heroism are commonly sought after.
Hints and Tricks
This strategy works because the vast majority of monsters before the temple are pretty easy. Even so, this approach calls for extreme cowardice. A temple diver should run away from pretty much anything not found on the first floor of the dungeon.
Spriggans are the quintessential divers. Their speed gives them the ability to run away from the vast majority of dangerous enemies.
Stealthy races may also be good choices for temple diving. Just remember that you are below your normal depth, and higher level monsters will usually see through your stealth pretty easily.
While diving, only use stairs to descend levels. Using trapdoors means you have no reliable way to run away.
If all pathways to the temple are blocked by difficult monsters, you can always revert to Plan A, return to level one, and start killing your way down. But there is usually a way through for the persistent.
If you get to the temple and your god's altar isn't there, it's often best to revert to Plan A. Overflow altars will be found between level two and level nine.
Note this is not for the faint-hearted, and players on a streak may wish to employ a different strategy. The low level mortality rate among temple divers is quite high. Fortunately, you probably haven't spent much time on a failed diver. Just start another!