Good progress!
The new cloud is much better; I did mine in sort of weird way.
If you want a cartoony style don't follow mine lol, I mean you could but something like the below images would be good. Vary yours from mine stylistically if you want, do your own thing and make it your art.
Different cartoon styled clouds:
And more obviously but just to give you an idea.
If you want to continue with what you have, I would make the shading on the cloud you made still less prominent, and give it some AA as I did in mine, but otherwise it's great. Make variations, don't just downsize it and make it darker as that looks sloppy.
Sun rays:
Ah, ok. Well, the only way to 'acquire' those skills would be to try. Do you have MSN or YIM? I can make some tutorials for you (videos) if you want to learn AA and the grass and the sun rays and such, although I could just post them here. It might help you to see how I work.
One thing I think you need for this mockup is depth for the sky; the two ways to achieve that (that I know of) would be:
A) Shade the sky. like so:
http://www.photoschau.de/images/20060329214426_blue_sky.jpg Notice how it gets lighter towards the bottom (technically the horizon)? Use artistic license and make it go
darker towards the horizon, maybe like this:
B) The sun rays. You don't need to get all fancy like I did; just one color will do maybe with some AA. Might as well try though it's your choice.
Random critique:
My cat animation is more than just goofing around; I fixed up some of your anatomy too. Look at the position of the legs in my kitty animation, that would be a natural stance (I believe) for a cat. Where you have the front right (our right) leg is weird and uncomfortable/tight. Loosen it up, check out some kitty pictures on Google.
Anyway, let me say one thing about the grass then I have to go:
Your tile looks better, but it looks a tad too realistic; simplicity, simplicity, simplicity! For this style go simple. Small amount of colors, simple easy-to-read shapes. Look at my grass; don't copy it lol, but I used only two colors (In the last image 3 akshully but the third was unnecessary) to shade the grass and two to shade the rock! Make it more like a happy condominium grass rather than a gritty realistic canyon grass. Don't copy mine tho.
Anyways I have to go.
Keep it up, see you around! And let me know if you have MSN or YIM.
Shrike