Took a while for me, but things got interesting when I started crafting. From there and I had to go deep mining to find metal, and then I crafted my first diamond tool. Down there I had a few scary moments, only survived because of the metal armor I did. Until now I'm not very fond of building, I just build the necessary. Tried to start some fancy stuff, but lacked a lot of materials, so for now I'm just filling some chests and crafting tools and small stuff.

Here's a good start for crafting: http://minecraftwiki.net/wiki/Crafting