Welcome to pixelopolis, first off.
About your sprites:
The grass and dirt tiles aren't bad, they're just repetitive. Get detailed. Try to define the blades of grass, and make a few different grass tiles to randomly mix in with the other grass tiles to break up to monotony. Same thing for the dirt. Add cracks, rocks, divots and ditches. Make dirt spots in the grass, etc. It's easy if you make a base grass tile, then duplicate it and place it next to the first grass tile. Then, make a dirt patch that spans over the two tiles. Add blades of grass (2-3 pixels high) randomly in some dirt spots (or in the dirt tiles) to make it look natural.
As far as shading the tent: First, I suggest changinbig the door into the tent. Make the lips of the tent doors fold outward, to look more natural. Then, shade where you think the tent might have natural folds / wrinkles / creases and put highlights on the p[arts closer to wherever your light source is coming from.
That's all for now, my lunchbreak is over and I have to get back to my job!