Here's some little tips to help y'all out with making high quality levels,Follow these steps and your levels will be on their way to greatness.
1. Have a theme for your level.
- Having a bland, and boring level with no real flair or theme to it is never good. Have some kind of 'gimmick', maybe. Perhaps I'm using the wrong word here, but what I mean is, use some of the many platforms you can find in the game. Or perhaps think of something using switches?
An example would be to have a level revolving around say, 4 platform spinners. Or spinning shapes, or ? switches, p-switches, or maybe a sewer revolving around the ground-pound panels? Employ your imagination, and be as free as you can be with the game's limitations.
Don't go too overboard, though. That can end badly...
2. Add 'twists' as the level goes on
- Here's something I do, and enjoy doing when it comes to level design. As the levels go on, you can throw in twists. Differing 'challenges'. Start off easy, with maybe a small obstacle course involving the main theme of the level. Then throw in a fun and creative twist to that theme.
Let's say you want... Seesaw platforms. You could have the player activate the platforms using switches, and make fun things off of that.
Or maybe you want moving platforms. You could throw in some Piranha Plants to spike up the challenge a bit!
Not much else to say here. I think you should get the point by now.
3. Have a difficulty 'progression system'
- Here's something. If you want a fun level, try to have the player slowly but surely grasp the main mechanics of your level.
Start it off with involving your main mechanic that you have for your level, to reward the player in some way - best way to do so is to provide them with a powerup.
Now that the player actually knows how the 'main mechanic' of your level works, have them go through a small and fairly easy 'obstacle course' involving the mechanic. Perhaps have moving platforms, that move at a pace not too hard to traverse, but not too bloody easy also.
Add in a few twists, make the level harder as it progresses. At the midway point, throw in a more major twist if you want. That's optional, though.
And at the conclusion of the level, aka the end/the flagpole, have the player utilize their new-found mastery of the mechanic that the level is based around, to reach the top of the flagpole and be awarded a 1-UP for their mastery.
Although, in almost all cases, you should make sure that there's a safer route to the flagpole. The 1-UP is optional, and a bonus - and thus should be treated as such. So have a simple route which won't take you to the 1-UP (top of the flagpole), and a route that utilizes the mastery of the level's main mechanic, which rewards the player with a 1-UP if taken.
That's a good way to introduce the player to the level's main theme, have them get good at it, then better, as the level goes on, and then to conclude it by testing the player's newfound mastery of the mechanic of the level. Good level design practice.
4. Have a select 'palette' of objects, that fits to the level
- Look at a level in NSMBDS. Or NSMBW, NSMBU, NSMB2 or Newer. Or almost any of the mainstream platformers in the Mario series...(and Newer)
You can see that they all have a select 'palette' of enemies, and platforms. They make sure it 'fits' to what the level actually is.
Let's say we have a forest. You could use Wigglers, Scuttlebugs and Piranha Plants. Main mechanic, Dorrie. Or four-platform spinners on tracks, over poison water.
Don't go overboard with your 'palette'- you pick one for a reason. Don't have Piranha Plants, Wigglers, Scuttlebugs, Buzzy Beetles, Spinies, Lakitus, Spike Basses, Cheep-Cheeps, Cheep-Chomps, etc. etc... That's a terrible palette! Try to keep it to a limit of enemies - best maximum for me is 4 enemies per level.
This also applies to powerups.
Try to think of what the player would do. Provide the player, in the level itself, with a powerup that would suit the level's 'playstyle'. If it's a cavern with lots and lots of enemies that you could easily kill with a Fire Flower and make the level slightly easier for yourself, you should...well, use a Fire Flower.
Or let's say it's an underwater level, where you could give the player a penguin to speed through the water.
Have a fitting powerup, which could fit with the level and make it more fun.
5. Have the terrain be more 'dynamic'
- Here's something important. Looks. Looks are important for your level. They add to the feel. You could have everything be perfect... But the terrain is terrible. You have 1-slope tile slopes. You have very, very basic edges, maybe even a few tiling mistakes.
The level stays at the top of the screen for too long, thus giving you a very ugly view of all of the tiles underneath. A repetitive, boring and bland view.
The floor is too flat. The ceiling is also too flat.
Avoid this at ALL COSTS.
Try to make the terrain feel 'dynamic'. Fitting. Have the beach terrain be smooth. Lots of slopes, and hilly. Add an amount of decoration that's not too much, not too little. Just right.
For a cave, perhaps have a more 'tight' (or, spiky) terrain. Especially with the ceilings - I like to make them all spiky-shaped, as to have 'terrain stalagmites'.
It's heavily opinion based on what you find fitting for your level, but it's your hack. You can go crazy all you want.
But just remember, don't have the terrain be too flat, bland and boring. It looks bad, and might leave a bad taste in the player's mouth/brain/level-playing quarters.
Also a quick not about slopes. They should generally start and end with the lesser steep slope object, and a steeper slope object in the middle. Just be sure to not make your slopes look too flat or boring.
6. Have Possible Rewards and Secrets
Since the number of star coins is limited to three, here is a list of other possible rewards. Clearly, it is quite short, so any other ideas are appreciated. Feel free to comment more ideas.
Everything Other Than Star Coins:
-Coins (Normal, P-Switch)
-Helpful Powerup (Normal, Roulette, Red Coins, Secret Yoshi)
-Easter Eggs (Something Like The 8-Bit Luigis)
-Pow Block (For Coins And Defeating Enemies)
When adding bonuses, they should be hidden or have small puzzles that must be completed to allow the player access to rewards. The best type of hidden reward allows the player to see the destination, but not how to actually get there.