The first class meeting sets the mood. If you receive a syllabus that is very detailed, you know to respond with work that represents this tone. Handouts may be given out. Some instructors are ready to start right away. How to be successful with the instructors.
Some instructors prefer to be formal, others are comfortable on a first name basis.
If the professor doesn't explain how they want to be addressed, ask them. If you do not know, try Professor Pascal or Dr. Pascal. Never misspell the instructor's name - just think how you feel when people get your name wrong. Be very polite, but persistent. Don't be afraid to ask questions.