Rule 1 - Keep your mouth shut.

When you are arrested or detained, you do not have to answer any questions except to give your name and address and show some identification if requested. As you may have heard on TV:
You have the right to remain silent.
Anything you say may be used against you.
These are part of your "Miranda" rights and you should take advantage of them. If you confess to a crime, it will be very difficult for any lawyer to get the case dismissed.

Rule 2 - Cooperate with the Police, but only to a certain extent.

For example, if you are suspected of driving under the influence of alcohol, you may be requested to take a test to measure the amount of alcohol in your system. If you refuse to take the test, your driver's license will be suspended. So you must cooperate. But if you are arrested for a more serious offense, and the Police ask you to "snitch" on someone else to get your case dropped, you better get a lawyer to make sure the Police hold up their end of the bargain.

Rule 3 - If it is a serious crime, get a lawyer as soon as possible.

If you are arrested for a crime, particularly a serious one, you should contact a lawyer as soon as possible. The lawyer can advise you on the bail process. Some attorneys are so familiar with the District Attorneys and Police that they may able to get the charges dropped prior to you even having to go to Court. Many times the District Attorney will "overcharge" you will several different crimes which they claim are Felonies. However, an experienced attorney can often get many Felony charges dismissed or reduced to Misdemeanors. Down the road, that same attorney may be able to get your criminal record "expunged" (which legally means it never happened).

Rule 4 - Make sure you trust your lawyer

Before hiring an attorney, you may want to interview several. Experience in this area is important. Do not hire someone that just passed the bar or that you do not communicate well with. Was the attorney trying to keep you calm or trying to scare you into paying a big retainer?. Does he or she have a strategy on the case? These are all questions you need to ask yourself after meeting with an attorney.