The 12

Don't be afraid to write an offer above or below the asking price. Offer what the market dictates.
Don't be surprised if you get Buyer's remorse at some time before closing... most Buyers do. It is normal and it will pass.
Don't buy before you do some comparison shopping... especially if you are new to the area.
Don't feel a need to negotiate if a property is fresh to the market, priced right and popular... the good ones often go quickly and at full or close to full price.
Don't get too many friends and family involved in your buying decision... you'll go nuts!
Don't shop rates after you've chosen your lender. Most Buyers regret they got seduced by the promise of a lower rate. After much emotional distress caused by time delays and hurried duplicate applying, the rate delivered is often the same.
Don't think all real estate agents and companies are created equal... they are not. Find an agent/company with strong service systems and support.
Don't wait for the perfect house... few of us buy our dream home. Compromise & prioritizing are necessary elements in home buying.
Don't wait for the perfect loan and/or price. If you find the right home... buy it.
Don't wait until you find a home to shop for the best loan. Get pre-approved first.
Don't work with more than one agent. Find one you like and stick with that agent. If you make a bad choice, change... but then stick with the new one.
Don't write an unrealistic offer. The Seller knows the market. Don't start the negotiation by slapping the Seller's face!