That is a very good question to be asking and the answer is not that simple actually. I have been using the auction very hardcore for 4-5 years now, and when I say hardcore, I mean spending a couple of hours on average each day browsing and checking listed items and their market histories. I'm not going to try to make a complete guide to using the auction right here in this thread, I'm just going to keep it very simple for now but if you want you can message me in-game and I can try to advise you regarding the specific items you are trying to sell.
Large stacks only:
There are some things that you should only sell in the largest stacks possible, like for example Metal Residue, Animal Oils/Hide and Socket Components. The majority of users of these things will typically be looking to pay the lowest mu possible and since they go through thousands of these things routinely, there really is no demand for the smaller stacks. That doesn't mean that smaller stacks never sell, they occasionally do, but I've had too many failed auctions to count at this point so I have totally given up on trying to squeeze out a little more money out of those things.
Smaller stacks welcome:
There are many things in the game that sell quite well in smaller stacks. Most of these are those things used in tier upgrades like for example Tier Components 1/2/3/4/5/6/7/8/9/10. These Tier Components sell so well in small stacks that I don't even bother with large stacks anymore. Others would include Garnets/Opals, certain resources used in tier upgrading like frigulite and typo... Up to you to research what else sells in small quantities, just look at the market history and pay attention to the dotted blue line (can't see it on yearly graph but can usually see it on monthly or weekly).
Specific quantity:
Textures (and skins), as well as paint should be listed in multiples of 323. Your 323/646/969 stack will most likely sell before others since 323 is how many you need per field when coloring/texturing an item. So a user will favor the 323 stack as that means no leftovers.
If you don't have the quantities required, your options are to save in storage until you do, or find someone that's willing to give you a fair price for your loot. I often do this for members of my society and this is a win-win for us all as they can keep cycling ped and I can add these things to my stack and usually make a bit of profit on it when I auction it. There are traders at Twin Peaks that buy a lot of things. If selling at a discount to these guys means you don't have to depo, it is an option that should be considered (save the depo fees).
Cheers,
Legends