For too many years, too many people bought too much house. How to avoid? Ron Liber in the NEW YORK TIMES offers advice. Put twenty percent down. This is the way it always was before banks threw out the rules. Get a fixed rate mortgage. Your monthly housing bill will remain stable. Don't spend more than thirty five percent of your pretax income on mortgage tax and insurance. Banks may not care if you spend more, but you should. Think through the expense of owning. Maintenance can easily creep over five percent of cost annually. And, best advice: always fall back on the eight-hour test. Whatever the size of your mortgage, you should be able to sleep soundly. If you're reaching for Ambien, it's a good sign the loan is too much.