My main thing that I look for in my levels when I'm making them is how much I enjoy it. If I enjoy my own levels, then chances are others will too.
Granted, I realize that's incredibly vague. The only thing I can possibly suggest is to play lots of other people's maps while making lots of your own. As you make your own maps, you'll be looking at other people's maps differently and learning things from their maps and taking them into your own. Over time, you'll also develop your own style.
This takes time, though. It took me a year before I made what felt like my first real level. I still don't think I have a complete grip on making a good level, even after four or so years off and on. Mostly off. If you're not putting in all this time because you're enjoying it, you absolutely won't. With your Halloween deadline, it sounds like you're just going to push yourself so much it's going to be a chore. Relax, open doombuilder, and have fun with it.