Critical-Gaming Network

Once everything in your level works smoothly, and you are done with making major gameplay changes, you're ready to enter the polish stage.

To polish a level, I prefer taking several passes over your work, checking and modifying one issue at a time. Keep in mind that these passes are not to be taken lightly. Each one requires your full attention and effort. The quality of your passes are directly dependent on your knowledge and experience of quality game design. I don't recommend doing them back to back. Instead I recommend taking a break and letting your mind clear between each one so you can approach each type with fresh eyes. Though there may be some passes that don't apply to the level you're creating, it's best to consider all of them.

Polish Passes

In no particular order....

Title, Text, and Information. Though it may seem obvious, it's important to ensure that every piece of text within you game/file is titled properly and grammar/spell checked. If you have the option, make sure the text is large/clear enough to be viewed easily. If there's a place to include creator information, be sure to put your name on your work along with the date and possibly a contact. Even if you don't plan on releasing your creation to the public, it's never a bad thing to take these steps.
Graphics. Scan over every inch of you level and make cosmetic adjustments to the visuals. As long as the changes don't affect the gameplay, feel free to alter the texture, materials, colors, and shapes to develop a unique look for you level. Even if you're designing a fictional world or a more abstract scenario (puzzle stages), you can still design the level with an organic look. Think of the levels in Bangai-O. Though they don't represent actual locations, the space aged and spaceship style keeps everything unified and convincing.
Remember the power of form fits function. Be careful to not include elements that look the same but have different functions. Be consistent with all the rules that govern the visuals in your level. If one spike hurts the player, then all the spikes and spiky objects should hurt the player as well. Don't use invisible walls. Depending on if the level editor is quantified, don't create obstacles that look like they can be cleared but are just outside the range of the player's abilities. In other words, if it looks like you can jump a hurdle, you better be able to jump the hurtle. If it looks like you can crawl under a space, you better be able to crawl under it.
Lights/Camera. Carefully examine every section of you level and check if the player can deduce everything they need to know from simply looking at the game to successfully progress. You may have to adjust the color and contrast so that the interactable/important elements stand out from the background, adjust the overall lighting of the level, or, if the editor allows, tune the camera for each section. Depending on the type of game, you might factor in the player's maximum movement speed. For example, in a 2D side scrolling platfomer, the faster the player moves, the less time he/she has to see and react to the upcoming obstacles and hazards. To remedy this problem, the camera should be zoomed out displaying more on the screen.
Sound. Because video games are a largely visual medium, about 80% of the information players need should be communicated through the screen. A large part of the other 20% is sound. Sound design is a subtle yet essential part of how a video game communicates. Because all collisions and interactions in a game are virtual or simulated, sound effects helps communicate exactly when and how objects interact. In addition, sounds help cue the player into actions that happen off the screen. If your editor gives you the power to customize the sound design in your level, be sure that every action, unique state, and type of interaction has a unique sound to it.
Balance is key. If you have control over the background music for your level or the balance between the sound effects and the music, be sure to adjust the sounds cape so that the sounds that communicate important information about the game world are pronounced over everything else
Flow. Flow is basically created when the level design doesn't get in the way of the player's forward drive. One way to think of flow is by getting into the mind of a speed runner. A speed runner is a type of player that seeks to get from the beginning to the end of your level as quickly as possible. Often times, doing so requires a more precise execution of mechanics and knowledge of the game. Keep in mind that redesigning your level to create an optimum pathway for speed isn't the point of this pass. The point is to watch out for and remove sections of your level for the purpose of smoothing the flow of the level for all types of players.
If you can, remove all elements of forced waiting from your levels. In Super Mario Brothers, each level was carefully crafted so that the player doesn't have to wait for enemies and other hazards to move into a good position before progressing. Everything from where the fire chains start their rotation to how Piranha Flowers reveal their position just as their pipes move onto the screen give players enough information and a window of opportunity to act without hesitation. Other examples of forced waiting include waiting around for elevators to arrive or doors to open.
Keep an eye out for areas of static space. Every action and moment for the player should be meaningful. Don't make players repeat an action too many times without that action escalating. Don't make the player travel through an area with nothing to do (usually happens with backtracking). Look at Super Mario Brothers World 1-1 as an example. Only the beginning of the level is blank. After that, every screen is filled with unique and interesting level/enemy elements. It's packed, but it's not cluttered.
Points & Secrets. If your level contains coins, rings, fruit, or points of any kind, go back through your level and make sure that their placement consistently reflects a governing rule. In Super Mario Brothers, the coins are designed to encourage jumping, provide a way for players to adjust their difficulty by going after hard to reach coins, and they're given as a reward for hitting special blocks. All the coins follow this governing design a feat that is essential for creating a sense of trust between the designer and the player. We all know that there isn't a coin in the game that the player can only obtain at the expense of their own life. Simply remind yourself of the function for your points and check every point to see if they follow the rule. The same idea goes for positioning secret items as well.

And that's all there is to it. It's a long process, but each step is designed with a clear and simple purpose.

Lessons 1 - 6 are all you need to start generating top quality content on your own. Feel free to boot up your favorite game/editor and getting hands on experience. Don't worry. There are still more lessons to come. Until then, stay tuned.