Judges will consider how much time passed between your court date and when you finally show up as a key indicator of your responsibility. If you missed your court date yesterday, be in court the next morning to explain yourself. If weeks or months have passed, your reasons for not coming back to court start looking more suspicious.
If you have a lawyer, call them asap.
You should contact your lawyers as soon as you know you can not make your court date. Your attorney can appear for you on most misdemeanors and can explain to the court about your absence and ask the court to "hold" a warrant for you. A "warrant hold" means that the judge may issue a warrant but it will hold it aside and give you an opportunity to get your client to come in.
Document your excuse.
Just like in high school, you can't say your dog ate your home work. You need written proof. If you were in the hospital, get a discharge paper. If your car broke down, get a car mechanic's estimate. etc. And don't appear in court and ask for an extension to bring the proof, that'll really show you got your act together.