This took a surprisingly long time for such a small and simple project. I get bored of looking at the same wallpaper very quickly and I had run out of pictures to use in my Pictures folder (there are 9,948 images in there, but I didn't try them all of course) so I decided to try making my own. Three days later I was finished.
As usual I sketched out a simple design and started making it Illustrator. The sketch was almost the same as the above image. The main idea was there would be different levels for each row of apps - an underground cavern for the bottom four, some grassy hills for the next row up, then some clouds, then the rocket, then a planet. The planet looked too realistic and it didn't seem to suit so I got rid of it. Once I was done I transferred it over to my phone and used it for about a day before I started to get annoyed by some things.

The first thing I noticed were the trees. I didn't like the round design and the small fruit was too small a detail for the simple style of everything else. They were also too well hidden and/or too evenly spaced, even though I wanted them to show between the apps. The other thing that annoyed me was that you couldn't really see any of the underground cavern, and the grassy hills were slightly too far down.

Aah, much better. Square trees are much nicer than round ones, and with the fruit gone they suit the rest of the image. I originally intended to have the clouds white or something and the red was just a placeholder so it would show up against the blue as I drew them, but they give off a nice early-morning vibe which I like (even though the sun isn't rising). There's a much nicer blend between the grass, dirt (originally a lame line that looked out of place) and rock. The cavern was still just slightly too low though, so I tweaked it a tad more.

Not a whole lot has changed since the first design, but I like it much more. The little textures in the grass, dirt and rock were drawn in Photoshop, as was the waterfall and the faint diagonal lines.

And here we have it. It's a pity that you can't see the bottom of the waterfall, because I quite like how that turned out. I'll probably get bored of looking at this after a while and make another one. I also have another 3D project in the works, but it's rather a tough one.