Kadamon said:
The randomly created worlds are beautiful, so I try not to touch on the little oddities I find. But screw sand and gravel, I don't want them.
Pretty much this.

I like to do a bit of scouting when I first spawn to see if there are any particularly cool environmental features, and try to build my first base around them, incorporating them into the architecture if possible. The entrance to my current "main base" is right next to this huge natural stone spire, which is a great landmark.
My usual play style tends to focus on massive spelunking expeditions, so most of my bases are underground anyway...I love stumbling across huge caverns while digging, and I'll carve paths into the walls wherever I need to in order to get at all the ore veins, but I'll usually fill them in if I don't need them any more and there's a specific look I'm going for. And yeah, I always replant trees once I've harvested them.
I'm starting to get a little more ambitious, though, and plan to start expanding upwards instead of downwards once I have a more definite idea of what I want to build. And there will certainly be expeditions into the Nether once I get the hang of obsidian farming. :3