So you want to make a solar system of your own?

First, open a new document. (I took 400*300 pixels)

Then, make the background ocean-blue.

Now are we arriving at the point where Xenofex is needed. Take Xenofex's 'Little Fluffy Clouds' Filter.

Instead of taking those cloud colors, pick an earth-brown as base color and a woody green as shadow color Shape the continents by adjusting the puff size, coverage and random seed. Surface hardness should be high and edge sharpness low.
   
Then, use the photoshop delivered filter 'Globe' to make the perspective changes. Use it at 100% in normal mode
   
Next, start selecting an oval (egg shape) at (0,0) and reverse the selection.
   
Delete the contents of this new selection and fill it black!
   
Now make a free transformation on this selection and adjust his horizontal size to match it with the real form of a planet.
   
Copy the planet and create a new, bigger document. (I took twice as big) Paste the planet and fill the background black,..., and the planet is finished.

To make it even more realistic, render a sun, add stars and some licht effects on the planet.