Listen to the following and you'll improve quickly:

Don't put gold right along the path - it's meant to offer an extra challenge.

Most people start with tiles first then add objects, but it's up to you.

Usually, less enemies is better, fewer enemies can offer a challenge without making it frustrating.

1 enemy can do the job of 3.

Don't lock enemies behind doors.

Watch where you put your trapdoors. If they lock the ninja in a corner or a place where you can't get out, it's a bad idea to place it there.

Feel free to ask questions.

Just keep mapping - You'll start to understand what makes a good map.

Always listen to advice from respectable authors.

Don't hide enemies or items.

Don't spam items or enemies or maps.

Only post 2 maps on Hot Maps at a time.

Play other people's maps. . . a lot.

Learn new things, and try new ideas and concepts.

If you devolp a style that works, stick with it if you want to. If not, that's fine too.

Playtest ALL of your maps (Can't stress that enough).

Anyway, Welcome to NUMA