1. Avoid making timely decisions
2. Change details, scope frequently, then become outraged at the increased costs, delays
3. Grill a contractor for solutions to a complex problem, then hire someone else.
4. Challenge your contractor's expertise with sentences like " it doesn't seem that difficult to me " or " my brother-in-law says...." or " my neighbor thinks....". If your brother-in-law is so good ,why not hire him?
5. Withold final payment for extended periods of time due to minor problems like missing accessories on back order. Project is deemed substantially complete when it becomes functional, triggering final payment.
6. Withhold final payment based on the assumption it will not be worth the contractor's time to chase the money down.
7. Cling to the belief that your contractor is out to rip you off, has X-ray vision to see behind walls that hide  faulty wiring, leaking plumbing or rot.
8. Poach the contractor's subcontractors to do side work after the initial work is complete. These guys are an extension of the General Contractor's repertoire and work for him/ her.
9. Schedule construction during the 3rd trimester of pregnancy, or while on vacation.
10. Buy appliances or materials at a discount online, then hold the contractor responsible for faulty or missing parts, delayed shipping etc etc. Our policy is; while we try to avoid this situation entirely,we charge to install client's material one time only without undue inspection/ modification. If the item requires additional work due to manufacturer's defect, delay or any other reason, expect to be charged accordingly.
11. Call the contractor late at night or weekends for a problem that can wait til Monday.
12. Hover over a job while muttering tragically " It just doesn't look finished" You're on a jobsite; it doesn't look finished because it's not finished.
13. Hard as it may be, try to keep emotion out of your disputes with the contractor. The only thing common to both perspectives is the financial aspect as well as quality of work and value for money. The relationship is a legal contract between a construction business (not him or her personally) and the homeowners. It is neither a marriage nor a divorce and greater success will be acheived by being civil first.
14. Budget sufficient funds for cost overruns; unforseen expenses happen, whether  material/ labor cost increases after contract signing date, or additional work requested, or unforseen problems requiring attention in order to proceed

Paraphrased from the New York Times, Joyce Wadler and Adrian Carter