Pay attention to all add/drop dates - check the Class Schedule. Sometimes dropping or withdrawing from a class can be the best choice available to you - so keep that option open by knowing your add/drop deadlines.
Attend class and don't come late, leave early, or leave at the break.
Know your syllabus. Remember that this is your road map for the course. It will tell you what you need to do and when you need to do it - refer to it often so you know you are staying on track. Know your instructor. Remember that no two instructors are exactly alike. Just because one instructor let you turn an assignment in late does not mean another instructor will. Each instructor has complete control over their own class, so be aware of what each individual instructor's expectations are of you - and if you aren't sure, don't be afraid to ask.
Know who your advisor is and be in contact with them, especially if you are having difficulty in a class (for whatever reason).
Use services on campus, like the Writing Center, Tutoring Services, Library Services, Computer Center, Workshops, and the Student Affairs staff.
Take your skill-building courses early on: writing, math and reading.
Pay attention to the level of your course: a 100-level course can be very different from a 300-level course.
Pay attention to the prerequisites listed in the class schedule. Do not take a course if you don't have the prerequisite done.
Take your assessment tests as soon as possible, so you will know which writing, math and reading courses to take.
Work with other students in the class. Identify a student or students who seem to be understanding the material well and ask to study with them - or to look at their notes. Form a study group that meets weekly - that way you know you will spend some time each week on the class material. You will be surprised how much you can learn from other students - and perhaps how much they can learn from you.
Slow down. It is better to take fewer credits and be successful, than to plow through your courses with poor grades. Remember, poor grades and a low GPA will follow you through your life - and may affect your ability to get into other schools, including graduate programs.
Talk to your instructor - about how you are doing in the class; about any difficulties you are having; about any course material or assignments you don't understand; about anything that is affecting your performance in their class.