Chess Puzzle Design

I've been thinking about designing chess puzzles lately and thought to give it a go. Have to admit though that it was harder than I thought and the outcome not as good as what I expected.

Have you ever tried to design a puzzle? If so, how did it turn out? I'm wondering:

• How does one approach designing puzzles?
• Does it happen when going through games and/or analyzing, and find a position interesting?
• Or having a theme in mind and trying to build the board from scratch?
• ... 

Here are a couple my tries (would appreciate any feedback):