Avoiding a 3 or 10 year ban.

 Be Honest, Be Prepared, Remember the Date.

Here is the rule about unlawful presence in its simplest form:

1.  If you are here unlawfully for 180-364 days, and you try reentering the country - you will be banned from reentering for 3 years.
2.  If you are here unlawfully for 1+ years, and you try reentering the country - you will be banned from reentering the country for 10 years.
3.  The deadly combo:  being here unlawfully for one year total (aggregate - add up any days you were here illegally, regardless of when), and then entering the country without inspection = Permanent Bar.  Don't do it. 

So the moral of the story is this
1.  Keep your visa current by either filing an extension or leaving the country in time.  No extension is available for those traveling on a visa waiver/passport.
2.  If you absolutely cannot leave the country in time, be very careful how long you stay.  180 days triggers the 3-year bar.

Other things to keep in mind:
1.  Memorize that expiration date.  Don't forget it.  Do everything in your power to comply (travel back or renew the visa).
2.  The official at the border will ask you the intent for your visit.  Make sure your intent matches your visa.  If you intend to immigrate, have the proper visa.  If you only plan for a short visit, have a tourist visa or a visa waiver/passport.  If you intend to work, have work authorization or employment visa.  You get the point. 
3.  Overstaying your visa by a day won't bar you from the country, but it makes life very stressful. The best defense is good preparation:  plan your travel in advance. 
4.  If, during your stay in the U.S., you need to change visas or want to immigrate, speak with an immigration attorney about your options.
5.  There are waivers for unlawful presence depending on your visa - ask your attorney about the benefits and risks.