Here's a simple tip that might help you alittle.

If you want an edge to be sharp, add another edge close to it. The closer the added edge is, the sharper the edge will be. See screen shot.

The cube on the left turns round when smoothed, but the cube on the right doesn't. I added an extra edge loop near the top edge, to keep the top edge from rounding out.

Note: if I added 2 edges, then the top edge would have been really really sharp.