I'm not sure what I'm meant to be focusing on. Nothing stands out.

I'd personally block out what you're going to have in the foreground and in the background before detailing.

Contrast is how you differentiate anything. If you want the backgrounds to be dark, then the playable area should be light, in contrast to the background. If you want the backgrounds to be low-detail, then the player area should be high-detail, again in contrast to the background. And so on.
Things that should be grouped together in the player's mind (different unplayable parts, different playable parts, unimportant things, etc) should not contrast from each other very much.

The player character blends into the background - that's super-low contrast. Make the character stand out, they should be always visible against the background (unless the gameplay demands otherwise). Two white eyes isn't enough to let players follow them easily. This could mean redesigning the player character entirely.

I highly recommend taking the time to look at some successful 2D games you like the look of. Analyse how they solved these problems, or how they failed to solve them.

Here's a revision from the previous work. Can't decide if I wanna go with blondie or brownie.

As you add details, remember that most of those details are still background details, and should be low-contrast. Some of your details currently stand out more from the background more than the characters do.

Bear with me since I don't know exactly what everything in your scene is, but here are some of the background elements that pop too much from the background:
The light blue/white rectangles on the left, including the sign
The triangle things with the red lights
The red lights in the bottom center
The yellowish lines in the upper right
All the green lights in the background
The cyan lines to the right of the portal

The characters, on the other hand, have dark blue clothing that's very similar to the background colour. Although their heads are clearly visible, the characters as a whole don't read well because they appear to be floating heads. If you want a dark world, you'll probably want characters in light clothing.

I think this reads a lot better! Because the buildings in the background don't have super-bright windows, the shapes of the buildings are easier to make out (dark colours tend to all blend together in the presence of very bright colours).

The characters stand out much better. I think the sign and white rectangles on the left still stand out too much though, being quite light compared to their surroundings. That's fine if they're meant to be interactive or otherwise important elements, but if that's the case, I'd also bump up the level of detail.

If you can keep the overall contrast low in the background, you can actually include more detail and stuff in the backgrounds if you want.

I recommend checking out Murder, a game with a futuristic urban setting that I think has a similar goal with its colours to your game. It has some issues with characters blending into the backgrounds, but other than that, I think it's good to look at in terms of overall colour use. It has many instances of bright colours in otherwise dark backgrounds, but the placement of these bright areas helps lead the eye around each level instead of distracting the player.
It also uses contrasting visuals to tell the story. Even where it does have low contrast, it has just enough contrast that different buildings read clearly and there's a lot of detail in the world without overwhelming the player. Some parts of the backgrounds are very bright and draw the eye more than the characters do, at least in stills. These are carefully kept away from the characters, and characters' animations help them draw attention away from these bright spots. The art in this game is worth studying, for its strengths and its flaws.

It's a point-and-click adventure game so its level design works differently, and that's important to keep in mind, as well.
(Though I recommend checking it out for the art, it's not a very good game. Unless you've got money to burn, I recommend looking at screenshots and playthrough videos instead of buying it.)

Decided to try some concrete stuffs



Is this working?

Tried an outline on the character and did some minor tweaks to him. Uhm, I don't have a weapon in the game, it's an autorunner with one touch jumping is all.

Revamped the buildings and am liking this much better.

This got a looot better!It is super readible, unlike the first mockups! Well done so far :)

Still getting a hold of this contrast thing. I think the background elements are better balanced though the character could use a little more separation. Any suggestions for this?

Wasn't satisfied with this and am still attacking it though I'm at a point where I could really use some guidance. I feel something is wrong with the scene but am not sure what direction to go. Any feedback is appreciated!