This looks like a living city. The clouds now look more realistic, but there is still this noisy outline you better fix.
The last step is to fix the bottom of the buildings. Look at this: http://www.hardcoregaming101.net/tmnt/tmnt_files/tmnttff-snes-clonefight-nes.png
I hope it helps.

I decided to use this thread to talk about my next sprites.

Today I started with something I skipped all the time, and that's a tree. Now I know why I skipped it, pixeling trees is terrifying.
I allready lowered the size and just made up a form for the tree top I liked.
But now I don't know what to do next. I tried a lot of possibilities for shading but nothing looked right. This is the best I got.

In all the tree tutorials they add the lighter parts first. Is this what I'm doing wrong? I admit, I don't have an imagination of the form of the tree. It blurred while the process.
Here's the tree without shadows:


Tomorrow is my day off. So your suggestions will be applied soon.

Welcome!
I also just joined this forum, and I can say that I really like your art style! I'm not very experienced with pixel art (only been at it for a month or so) but I think your shading is very good. I think this forum is a great place for you to post all your ideas! For the last sprite you posted, one way you could make the hat look more like straw would be to make a few pixels stick out. I think all the colors you picked go pretty well together. To answer your last 2 questions you should check this link out.http://pixelation.org/index.php?topic=5624.0
I'm not German sorry  I think you English is very good! Welcome again 

Thank you AppleGirl! I hope to see more of your art in the future. The hat's on my agenda now. I like your idea with the stalks and I'm going to try how it looks . BTW: It's a wolf. ^^"

Dude,i'm pretty sure that all of the nice people here are waaay to better than me doing pixel drawings, but since i posted my first thread i've felt really comfortable, so i'm very excited to see what are your thoughts and work.Since you are one of the newbies like me, can i give my opinion on your drawings? You do have for sure a large variety of styles, like that palm tree,passing through the mushroom and the doge, your art is very versatile.

and by the way...

 your dog is NEAT.

Gonna name him to myself as Barry.

Hi Fieldren! Your critiques are very welcome. Please don't degrade yourself. Your seemingly strong will and your imagination will let you create great art. Just don't stop.
Maybe we can encourage each other from time to time. That's what this forum is about, right?

I'm glad Barry got his name. Now I can write something on the sign at his cage, since he is a wolf.
(See the answer for MysteryMeat for more informations.)

Hello, sorry I missed this thread until apple bumped it! I'd say the first step would be to do normal art first, the first step is knowing the how-to draw. This is coming from a person who started doing pixel art before he started drawing like a normal person first, and let me tell you I wasted a lot of time grinding those gears before I started paying attention to such alien concepts as "Basic anatomy" and "proper shading".

For that end, I recommend starting with the Loomis guides, which are easily discoverable through google. He's an excellent resource for artists of any skill level, his books on figure drawing and fun with a pencil both EXCELLENT tools for people trying to get a grasp on the basics, which are always worth revisiting from time to time.

As for feedback on your current stuff, avoid dithering so much when you shade unless you're going for a texture! For example, on the apple it makes it look like there's bumps on the skin. Instead, look at the pixel clusters part of the general art help masterpost here on the forum! It can help a lot, but the basic idea is to try and keep like-groups of pixels "clustered" together rather than have them spread out as you would with dithering. It creates a smoother, more uniform look overall!

Next, work from reference even for pixel art! It took me a while to figure out that that was a bat, the wings look like beaver tails with how rounded and uniform they are whereas in reality they tend to look like webbed arms!

Hi MysteryMeat! Thanks for your time. Nothing to apologize about. It's not like I paid you to answer me or something.
I started to train my drawing skills two days ago, as you (and some other user of this forum) are advising. I decided to follow "drawabox" as it fits better to me. But there is no reason to try some of the sketches of Loomi later on.

The apple is a one of my first piece. I don't think I'm going to fix it, because I want to look forward. But your tip is very welcome. You don't need any theorie to see what the dithering has done here. But I will not forget about pixel clusters in my future works.

Let's come to your last lesson: As everyone considers my wolf a dog, I got your point. See what I've done to the bat. It's just a short workaround because the whole pose isn't right. But I felt like doing something with all your suggestions. Thanks a lot.

I feel very uncomfortable with the clouds.
It just makes no sense. I lived in the city my whole live and I can't recognize to see clouds like this at night.

Hello dpixel! Sorry for the delay... I had no access to computer til now due to travelling.

Thank you so much for the tip! the color and pose you were using are so much more natural. I am trying to do a no outline approach so let me use your tip and fix my character haha.

Use outlines. They help a lot. I know there is cool stuff without them. But as a beginner myself, I can give you this advice. Outlines make pixel art a lot easier and there is a limited number of styles that support that kind of spriting. There is no need to push yourself to something that is hard to achieve at your current level. Learn to make good sprites with outline and come back to this idea later, when you feel more comfortable with the basics.
Sorry for the offtopic.

EDIT: I've search your recent posts. You've come to far to change the style now.
So just ignore my babbling.