All too often people willingly give up their rights bc they erroneously believe that those rights only apply to criminals. Let me clarify: they apply to innocent people too and you should guard them jealously. Here is why this is so important...
A. Do not agree to give a DNA sample. Ever. Do not fall for the "rule yourself out" line. If they need to ask for your consent it is likely that they do not have enough to apply for a search warrant. If they do have enough then make them go get one. Think DNA is always correct? Wrong. Those labs are operated by humans who make mistakes. I'm not talking theoretical. Labs have an "unexpected results" log where they keep track of problem results. This includes cross-contamination in the results and sometimes that contamination is the testing scientist's own DNA. This happens more often than people realize. If you give a DNA sample you introduce your DNA into the lab where it may end up mixed with some evidence. And once it's mixed it can't be unmixed. Do not risk it. Make them get a warrant.
B. Crime labs are not perfect. Google "Saint Paul crime lab" for one example of awfulness.
C. Talking to police w/o a lawyer is a bad idea even when you're innocent. Say you were driving your red sedan on Main on Monday by the local Target. You are a white guy with a blue sweatshirt and blond hair. You are stopped by police a day later and they ask where you were on Monday. You did nothing wrong so you tell the police where you were. But you don't know that on Monday a white guy w/ blond hair and a black sweatshirt was reported as robbing the Target of on Main. He drove away in a red car. Oops. Looks like you just made yourself a suspect despite not doing anything. Next thing you know you are in a line-up. Oh and eyewitness identification is really unreliable so you are ID'd by the witness. So don't talk yourself into a bad spot. If police want to talk to you the magic word is "lawyer." Use it.
D. Do not let them search your car, purse, bags, etc. A MN woman was charged w/ drug possession when police found an aspirin in her car. Don't do that to yourself. Again make them get a warrant.
E. If you are in an interrogation room or in a room at the police station you are almost certainly a suspect so don't talk. "Lawyer."
Rights are for everyone. Innocent people should use them and realize they are there to protect them. Do not give them up!