If you've been pulled over by law enforcement in Illinois, you should give your license, registration, and proof of insurance when requested, and then invoke your right to stay silent immediately. You must comply with all lawful orders, but you do not have to speak and should choose not to. Offering up information accidentally can turn a difficult time into an impossible one, very quickly.
You will be asked to submit to a breathalyzer and maybe even field sobriety testing. These tests are both less than 80% accurate, so you can refuse to consent to them. If you refuse to consent, however, you will be arrested immediately and later be required to submit to chemical testing after you are booked. You will also have your license immediately suspended. If you take these tests and fail, you will also be arrested immediately and charged with a DUI. If you pass these tests, you will hopefully be free to go, though you may be charged with other misdemeanor charges, such as reckless driving or speeding, etc.
If you are being pulled over and given criminal charges, try to remember everything you can during your questioning and subsequent arrest. From the names and badge numbers of the police officers to any possible witnesses or cameras nearby. Every detail can be vital in clearing your criminal records.