Don't run or try to escape.
If you are driving down the street and the lights come on, pull over as soon as possible and remain inside your car. Do not give the officer a reason to charge you with evading arrest. If the officer simply pulled you over for a traffic violation, you may be issued a ticket and allowed to leave without being questioned further.
Keep your hands out of your pockets.
The quickest surefire way of giving an officer an excuse to search you is by putting your hands in your pockets or reaching under the seat. The officer will say that he searched you for officer safety and not because he thought you might have drugs on you. An officer thinking that you have drugs on you is not enough to allow him to pull you over or search you. This is the number one reason that police list as their justification for conducting a search without seeing or smelling drugs. The police will report that you made a "furtive movement and he was worried you might have a weapon." Unless there is a video, it is your word against the officer. 9.5 times out of 10, a prosecutor, judge, or jury will believe the officer over an accused.
Be polite to the Officer.
This goes without saying, but if you speak properly to an officer and show respect, then you have a better chance of him not thinking you may have something illegal in your car or on you. However, being polite and courteous does not mean telling him that you have something illegal when you are asked. Chances are that if you never tell him there is a pound of marijuana in the trunk, he will never have an excuse to look for it.
Do not give the police permission to search you or your car.
This is not a game of poker and the police are not bluffing. If they ask to search you or your car it means that they do not have a legal right to search. Do not think that if you say yes, then the officer will just think you don't have anything to hide and leave you alone. He will search your car, he will find the dope, and he will take you to jail. If you say yes to a search, then you are giving the officer "consent" and that is all he needs for a legal search. I don't care if the police threaten to go and get a drug dog or a warrant. Tell them "no" that they can't search. Chances are that by the time the dog gets there or they actually get a judge to sign a warrant, you will have been detained for a longer amount of time than the law allows. If the police keep you for too long, they violate your rights and drugs will get thrown out by a judge at trial, resulting in you winning your case
Do not admit to ANYTHING.
You have a right to remain silent. USE IT. The police officer is not your buddy. He is not going to let you go and just throw away the drugs. The police will try to act cool with you and say something like, "just tell me where the drugs are, it's no big deal." This is a huge deal! He is trying to build a case against you, let him find the drugs. Even if drugs are found, admitting they are yours does not help your case. Even if drugs are found in your car the police still have to "affirmatively link" them to you.
Hire a good lawyer.
If you are hand cuffed, put in the back of the car, and on the way down to the station, there is nothing that you can do or say that will make the cop change his mind and let you go. You need a good lawyer. As soon as you bond out of jail, start setting up some appointments with lawyers. Find a lawyer that will quote you a flat fee that is experienced in defending drug cases. Make sure they at least sound like they know what they are doing, and have actually tried cases to a jury. This is your future that we are talking about. You are not going to find a good lawyer to represent you on a case involving a kilo of cocaine for $500. It will not matter when you have a criminal conviction on your record or are spending time in prison that you saved a few bucks.