Do you not hate the inevitable death you must face, whether it be from a random spike, or an impossible level? If you wouldn't play it, do not build it, I'd say, as you actually can play your own levels if by some rare chance one of them is chosen.

You load a level, one life remaining, a spike spawns before the light from it has a chance to get to your eyes. We've all been there, right?
When making a level, be sure not to place enemies, traps, or anything that causes death in areas that will kill the player upon start. If your map is highly detailed, this should be even more followed, as the players may not even know where the entrance is before they die. If your player can stand at the starting point for ten seconds or more without dying, then your level should be fine.

If your level features some sort of timing system, be sure that the timer is not started immediately after the player starts the map, but instead, uses a switch to start the timer which must be used before the player can move on, allowing the player to see the level before the timer starts. This is especially true if your level is highly detailed, as some people like me sometimes cannot even find the starting point until five to ten seconds later.

Teleporters.... They are definitely fun, but using more than two of the same type can also allow the map-maker turn the game into a life gambling machine. If you've been playing for a few hours, you probably have already seen this. Do not make maps where there is a chance the teleporter you are forced to take can take you into a pit of death. An optional gamble to the end of the level? Fine, but please do not force it.

Make your levels fair to those who have no more skips, or simply make levels people will not skip. Even if those pixel-perfect jump levels can be super-cool, levels which are too hard are like a wall in the dungeon. Impossible levels are even more so a wall. Ask yourself: "If by any chance I came across my level in the dungeon, would I skip it?" If you want people playing your level, until/unless some sort of difficulty setting is added, keep your levels at least reasonable.

Do not make maps that require exploiting bugs to complete. If the used bugs are fixed, then your levels might become impossible or very hard after an update, possibly rendering your level as spam. (Not sure if updates are ex post facto on levels, but I included this just in case)

We have all seen those happy levels with coins everywhere, a free heart, and a smiley on all four corners. These are not necessarily a horrible thing, but they may disturb the hardcore players. To be safe, make a secondary route in your freebie levels which leads to the exit, creating a challenge on that route which also provides extra coins. However if the troll-map issue is solved, these happy freebies will basically become spam as they have nothing else to neutralize.

Here is an example of an optional bonus level if you feel it must be done:

Do not have useless things in your map. "Trash" does not necessarily refer to enemies that serve no purpose, as the start of the dungeon has those, but the enemies which die immediately, are not aesthetically pleasing, or are too plentiful. This is mostly for aesthetic and quality purposes, but can also cause lag. You know that monster that flies around and rams into a spike before you can even look at it? Do not include it. Another thing to note is limiting moving obstacles. Is your entire level made of wooden or metal boxes that serve no purpose? Do not even think about publishing it. Do not include too many moving things that serve little to no purpose. Do not create an entire row of enemies when all you need are a few and you cannot jump over them.

Continuing from the last section, take out the laggy trash. Seriously, do it. Lag may sometimes give superpowers such as being able to pass through enemies, and even some types of blocks, but they are inconsistent and make the level basically a gamble. If your level lags to the point where this happens, remove stuff. Lag will NEVER make fun levels due to its inconsistency (unless you are that guy who can do anything since you are just that guy).

Levels should be fun. Do not make levels where the player sits in one spot for three hours to jump onto a platform. I'm not saying to not put breaks in your level, but do not have half the level the player just sitting there waiting for the platform to move. Maps like this are quite frustrating when you die since you must go all the way back using the platforms which take five hours to arrive. I know this is not easy and possibly not the best idea for some sections of levels, but at least try to keep the player doing something. Not everyone is patient like you. Try to make levels that can be completed in one quick and fluent run, without the need to wait at most three seconds for anything, if you can.

If you are any decent player at all, there are a lot of levels you do not even bother to look at. You probably already know what I'm talking about. Do not post levels which serve no purpose. Do you have level with a bridge? Just a bridge. Nothing else. No enemies. No coins. No hearts. No obstacles whatsoever. This level may look like a freebie, but is also basically a spam map which reduces the quality of the player's dungeon-diving experience. Art levels are not real levels! If you really want to post that bridge anyways, at least add a single coin and an enemy! (These maps which contain absolutely nothing are not very common from what I've seen, but they are still existent, so I thought I'd address them.)

Challenging or good-looking levels aren't always good levels. They could just be skipped. Be sure to make your levels so that they are the best they can be. Have a good challenge-reward ratio. Do you have a seemingly impossible level? Fill it with coins! Have a level which is just a bridge? Well, you haven't been listening and you should get out. The harder the level, the more coins you should add. Make a level that if you'd see, you'd want to play.

Originality is key. Do not copy and paste levels made by other players, even if you do give credit. Copying will create a repetitive experience which causes the player to feel as if their time is being wasted. The more original, the better! That is not to say every level has to be on two opposite sides of the spectrum, but to say levels should not be basically the same. Have a set of puzzles? Fine. Have a set of very similar puzzles? Probably not a good idea. Remember that the point of map-making is not just making a map and setting a difficulty. Maps should be fun and rewarding, no matter the difficulty (unless there is no difficulty, then you might have a problem)..

Are there any other things I forgot to mention? I know this probably won't help with 99% of the troll maps being created, but I thought I could try to help a bit.