The first and foremost skill required to resume a college education is determination. Whether or not you like school, putting in the extra hours to attend class, do homework, and prepare for exams is still a lot of effort. Without a determined attitude, these will cause you to lose interest and stop your education. Once you have made a solid decision to see this through, there are certain other skills needed to do it well.
Taking good class notes is not always considered a skill, but for students it is critical. Most students are not able to take down lectures in perfect shorthand. Even if this can be done, it will take too long to distill all of that lecture into its important components later. It is better to be able to pick out the important from the unimportant during the lecture.
If you do the reading ahead of the class time, it frequently will help you to make notes of only those portions of the lecture not already covered adequately in the text. You will also be able to notice areas where your instructor may differ from the text. This will require that you ask a question or two for clarity. It might be that there is new information, or it might be that the instructor believes that his or her information is better than the text. When the test comes, follow the instructor.
A good student must be able to make good outlines and word lists from the text. You need a general understanding of the material and its organization. An outline will do this for you. Vocabulary is another big item. Developing word lists and definitions will help cement this material into your memory. Starting early in the semester will give you time to do a good job with this.
Time management is a big consideration. With multiple classes to juggle or a job and school, finding the right pace to accomplish everything is important. Wasting even a week can cost you a letter grade or two. Begin working on your class as soon as you have the syllabus and textbook in hand. Make final notes each day from your lecture notes while your memory is still fresh. This will reinforce what you heard and make your notes more accurate. It will also give you an idea of gaps that you may need to get from classmates or from in-class questions.
If you know that you will be facing math classes, and your math is rusty, find a way to brush up. Algebra is not really that hard. You just need to get a good remedial algebra book and do some serious review. Whether you are going to face a formal math class or not, you will need the math somewhere along the way. So, get this skill back on track.
Work on your reading skills by forcing yourself to read something besides a romance novel or western. Pick up a classic or two and dig through them. It will pay dividends in your reading comprehension. At college level, you are expected to be able to read material and understand it. If your reading is weak, you just need to practice. Keep a dictionary handy and look up those words that you do not know.