This tutorial will teach you how to create you own world from nothing but a blank canvas.

first create a new document, i will be using 500x500
Fill the background with black then create a new layer.
Set you foreground colour to a bright green and you background to black.

Then run FILTER > RENDER > CLOUDS. and you should have something like below.

the next thing we must do is go to FILTER > RENDER > DIFFERENCE CLOUDS. You image should now be similar to the one below

FILTER > ARTISTIC > CUTOUT is our next filter, use settings like the ones below.

You should now have something that's similar to this.

Using the magic wand tool, select the large solid colour area, and fill it with a nice light blue, you should now have something like this.

Using the marquee tool. Holding down shift to create a perfect circle, make a selection like below. be sure to get a variation of the "sea" and "islands" into the selection.

Press CTRL+J to duplicate the layer.
Delete the first layer, and you should be left with something like below.

Go to FILTER > DISTORT > SPHERIZE. and use 100%

While holding CTRL click on our globe layer in the layers pallet.
This will create a selection around the globe
Go to SELECTION > MODIFY > CONTACT, and use 3pixels.

Press CTRL+SHIFT+I to invert the selection, and then FILTER > BLUR> GAUSSIAN BLUR and use 3px.
Press CTRL+F three times, and you should have something like the image below

create a new layer and call it CLOUDS. Reset your colour's (keyboard short cut "d") so that you have black as foreground and white as background color.
Then you need to apply:
FILTER > RENDER > CLOUDS
Followed by
FILTER > RENDER >DIFFERENCE CLOUDS.
And you should have something like this.

Using the magic wand tool, select an area that is mainly black, then right click and choose SIMILAR. and you should end up with a selection like below.

Press CTRL+ALT+D, use a setting of around 5 pixels.
Hit delete and you should have something like this.

CTRL+CLICK on our WORLD layer from the layers pallet
then let go of CTRL and just click on our clouds layer from the layers pallet. What you should now have is the selection the same as the world layer, but active on the clouds layer.
Proceed to FILTER > DISTORT > SPHERIZE and use a setting of 100%, you should now have something like this.

Add a layer style to our clouds layer, PATTERN OVERLY is the only effect we are going to apply, for the pattern choose the CLOUDS texture.

Reduce the fill off the clouds layer to about 70% and you should now have something like this.

Press CTRL+E to merge the clouds with the world layer. Duplicate this layer and call it WORLD TOP. Select the bottom world layer and go to FILTER > RENDER > LENS FLARE. and move the FLARE CENTER into position and use the same settings as in the image.

You should now have something like this.

Make sure you don't have any selection active and go to FILTER > DISTORT > SPHERIZE, again use a setting of 100%.

That's the basics of creating your own world, Just have a play around, and you will be bale to modify the process to get a much better outcome. here are some alternate outcomes.