I figured I should share some of my survival tactics. I'm sure others have thought of these, but I haven't seen them anywhere yet. They are in no particular order.

When to identify things

If you pay attention to what you drink/read, you will know what types of potions/scrolls are left unidentified. For example, if you only have terror, lullaby, and psionic blast unidentified, then you know there is no reason to read any unknown scrolls except during a battle. It is a small, but useful, advantage.

Unidentified health potions are cheap to buy

On games where I get past the Goo, it isn't unusual for me to make it through the sewers without using a health potion. To improve your odds of doing this, use Sungrass seeds to heal up when possible, along with frozen meat, the sungrass plants found in garden rooms, etc.

Shops seem to always have at least one health potion in them. If you make it to floor 6 without identifying your health potion, you know one of the potions in the shop will be it.

To further increase your odds of reaching floor 6 without identifying your health potion, consider skipping Piranha rooms on floor 4 and returning to them after buying out the unidentified potions in the shop. Throw things on traps instead of trying to guess which potion is levitation. Use seeds of firebloom or wands of firebolt instead of potions of fire on wooden barricades/bookshelves. If playing as a huntress, prop the Piranha room door open and kill the Piranhas with your boomerang, which saves you an invisibility potion, gives you mystery meat to freeze, and keeps you from accidentally drinking a health potion. (This can also be done by any character with a wand of teleportation.)

If you make it to floor 6 without identifying your health potion, you should now find a way to identify it without actually identifying it. This is done by killing flies until one drops a potion- now you know without a doubt which color is healing.

All this work nets you an extra +100 gold in the shop on floor 6 for each health potion you can buy unidentified, and it nets you even more money if you make it to floor 11 or 16 without identifying your health potion. But much more importantly, it keeps you from wasting a health potion before you actually want to drink one.

Buy stuff and sell junk

Particularly in the first shop, you should be buying almost everything there. Unidentified potions and scrolls are great- buy them up for cheap, then use them to figure out what they are.

Lloyd's Beacon is invaluable for shopping; set it to a square just outside the shop and use it to hop back later to sell or buy again.

Sell scrolls and potions you don't need. Everything can be useful, but often you'll have things you won't use. For example, fire darts do practically no damage; you hit for 1 and a creature takes 3 burning damage before the fire goes out. You may get lucky and the creature burns for 5 turns or more, but I usually sell them for guaranteed gold instead. Likewise with darts. (Re-evaluate this advice if you have no other distance weapon.)

Many of the armor glyphs have serious downsides. Rather than trying to get lucky with a glyph you actually want, you can sell Arcane Styli and forgo the risk of getting the wrong glyph on your best armor.

Any character with good wands, or the Huntresses with her boomerang, can often sell Shurikens or other distance weapons they will probably never use. Some wands have precious little use. For example, Wands of Flock and Wands of Telekinesis are so situational that I typically sell them. Evaluate what you have, whether you will use it, and if not, sell it.

Never sell seeds. They don't get much gold, and you can turn unused seeds into potions.

Don't buy weapons or armor; these are overpriced. Don't buy Ankhs, as you only resurrect with your equipped items- that means no healing potions, gold, or food. Usually, that just means you live an extra floor before dying again. Save the money (and the inventory space) and use it on something to keep you from dying in the first place. Buy food rations only if you are low on food.

Transmutation Wells

Main article: Well of Transmutation

Typically, people say you should use upgrade scrolls on Wells of Transmutation, then enchant a weapon, but I find this is often a time-consuming and risky endeavor.

Consider using these rare wells for a less risky, lower-investment option.  If you have, or expect to soon find a strength potion, they are candidates for transmutation.  You can always turn a weapon into another weapon of the same tier, which is great for turning that amazing Glaive +5 into an even better Warhammer +5, or for combining weapons with the Troll's quest.  Rings, or wands with little use, like a Ring of Energy on a character without any wands, could become a Ring of Haste.  If you are feeling lucky, you can even drop in a potion, or a scroll, and see what comes out.

Scroll of Challenge - Goo Strategy

Main article: Scroll of Challenge

I used to think these were worthless, but I've revised my opinion of them. Plant multiple seeds of pain in the corridor outside Goo's door, then use the scroll to bring his death. A huntress in a long corridor, or at the end of a room with only one door, can use this scroll to bring enemies in and pick them off. Any character with a potion of poison gas can read the scroll and then throw the gas strategically, forcing many mobs to take significant damage before ever reaching you.

Skip the Demon Halls

Literally, don't play them. Save up three magic map scrolls and use one on each floor. Walk in the hallways from the starting stairs to the stairs down, and if possible, don't fight anything. Mind Vision potions can help you avoid critters.

There you have it; some tips I haven't seen around, that folks may not already know about.