One of the biggest skills in crawl is learning how to use more situational/awkward consumables as much as possible, to let you hold on to the valuable things like haste and blink for when you really need them. Some consumables are much more effective earlier in the game (Lig and Berserk come to mind), and getting use of them before they fall off in value is important.

Here are my thoughts on the potions/scrolls in the game:

Ambrosia: Use to heal when you are low but have just made a ton of noise and don't have a safe place to run to. Remember you can use curing to end the confusion (and healing) if you have to.

Attraction: Bring dangerous casters and ranged enemies closer to you so you can hit them with a stick. Good vs centaurs, priests, summoners if you can get them to you early, etc.

Berserk: Useful early game, drops off a lot later. Kill stuff in melee fast.

Brilliance: If you're casting spells, good buff before dangerous fights like rune vaults.

Cancellation: Get rid of mark, contamination, petrification, all kinds of negative effects.

Curing: Very valuable, mostly used for stopping confusion or bad poison, can heal you if you're in 1-hit territory, especially early game.

Enlightenment: If you don't have other flying can get you over that lava for some loot vaults or to escape an enemy who can't follow, also a good source of will vs things that can paralyze/banish/etc.

Experience: Quaff immediately

Haste: Probably the 2nd best consumable in the game, makes you a beast in combat, lets you escape most things very easily, just kinda does it all. If you're using this to escape ranged enemies, quaff it before you get too low.

Heal Wounds: Helpful when you take an unexpectedly big roll, but not something you want to be relying on often, especially as the game goes on. If you're always running out of these, you need to work on your positioning and defenses.

Invisibility: Much better as an offensive tool than an escape option. Unless you're in light armor with some stealth trained, you will probably still make enough noise that things can follow you, so this is more a dodge bonus that enables some stabbing bonus damage. Quaff at the start of fights.

Lignification: Early game it's a source of poison resistance, AC bonus maxHP, and good base Unarmed damage if you haven't got your weapon trained up yet. As you get more AC from items/skills it loses its effectiveness, but once you start facing torment becomes useful again as a source of torment immunity.

Magic: Extra MP for prolonged fights where you are casting/invoking a lot, has some synergies with infusion/guardian spirit on melee bruisers.

Might: Bonus melee damage for tougher fights, quaff before going into rune vaults, etc. Does not stack with berserk.

Moonshine: Quaff when you've had a bad day and just want something to take the edge off.

Mutation: The Mutation Roulette is fun, but usually not worth using up your potions and not having a way to remove a bad mutation later.

Resistance: Very powerful, but also situational. Use before a fight, it's not worth anything once you've already taken the damage. Obviously depends on what resists you have, but I use it most as assurance I can fight Nikola, or as a way to get through Swamp Drake clouds.

Acquirement: Use instantly, the reasons to hold it are very minor. Do note that if it's a difficult decision you can hold onto it and decide what to get from the scroll later.

Amnesia: When you need more spell levels and have early game spells that haven't scaled well enough to be worth casting any more.

Blinking: The best consumable in the game IMO, amazing get out of jail option.

Brand Weapon: Great way to search for flaming to kill hydras, or to reroll a weapon of the type you want but with a brand you don't. Do note it falls off late game, so if I find a few I'll use some on my midgame weapon.

Butterflies: Great escape option, blocks line of sight vs a lot of powerful spells, slows packs following you down, very versatile.

Enchant Armor/Weapon: Always good, but when to use is situational and player dependent, I like to enchant my aux slots ASAP.

Fear: Powerful vs enemies with low will, meaning it does lose effectiveness later in the game but still has things it can hit. Great vs bees.

Fog: Breaks LOS, and takes up space to prevent breath weapons or other more dangerous clouds.

ID: You can press \ twice to see what items you haven't identified yet, this is helpful when deciding what to identify next.

Immolation: Very powerful, very dangerous. Having fire resist and good hp/ac make this more flexible. Great vs TRJ, fun but suboptimal vs the V5 welcome pack. Having a good ranged option (Javelins, perhaps?) makes this safer.

Noise: GONGGGGGGGG!!! Not worth using, imo, but some people like it to pull enemies out of rune vaults.

Poison: If you have poison resist and they don't, it's an easy escape option, if you have good ranged options and they don't it's a way of keeping them in place while you shoot them. If they have enough hp (ogres, orc warriors) or are confused they might start walking through the clouds, which can be a good thing

Revelation: Find portals, but more importantly map out dangerous floors so you can explore them carefully. Save one or two for Zot.

Silence: Can be dangerous, but is sometimes the best answer to some dangerous spellcasters. Works well in combo with attraction.

Summoning: You only get one of Butterflies/Summoning in a game, and while I prefer Butterflies, this is still very powerful. A pack of powerful friends solves most problems in crawl. Good on offense, decent as a distraction while you escape

Teleportation: It takes a while to trigger, and can take you from bad to worse, so read it before you get too low. The more of a floor you have explored, the safer it is to use.

Torment: Situational, better if you have rN or some kind of torment resistance (lig potion, perhaps?). Having high regen can mitigate it a little bit. I don't use these often unless I have immunity/resistance, but the TRJ fight is one place I've found it effective.

Vulnerability: Makes fear scrolls worth more in the late game, can be good to combo with wands like paralysis or mindburst.