Here are some bad habits I've noticed:
1) Not understanding how difficult it's going to be to start a business.
2) Underestimating how long it's going to take to get off the great. Lots of new business owners love their idea so much they think it's going to take off right away.
3) Not understanding how much marketing is involved with starting a successful business. Even if your product is great, you've got to figure out how to get it in front of people so more people can find out about you and decide whether or not they want to buy.
4) Underestimating how much they'll need to charge. Example: "Professional photographers charge $2500 for a wedding? I can undercut that by $1500 and steal all of their business!" Reality: People charge what they do not because they're gouging people but because that's what it takes be profitable.
5) Not focusing enough. It's easy to want to sell to everyone, but it's much more important to find a profitable group of customers, be awesome for them, and then branch out to more customer groups rather than trying to be all things to all people.
6) Not realizing that you haven't picked a profitable business. Just because something's unique doesn't mean there's a market there to support the business. Not only do you need something unique about your business that helps it stand out, but you also need to make sure there's enough of a market to support your starting a profitable business.
These are all the things I could think of off the top of my head.