Alright, here's my problem. I'll create a tile like this one:

Looks fine as a single tile, right? (for the sake of this topic, let's say it looks fine.

)
But when I line them up 2x2, it looks bad:

So, I guess I'm asking for help with making tiles transition into each other without being able to detect a lot of repetition.
Also, I need help with creating depth in tiles. Making the rocks look like they're kinda rising out of the ground...I really want to get better, so any and every peice of help is greatly appreciated. Feel free to edit my examples.