It doesn't matter if you're a first semester freshman, a senior about to graduate, or an adult returning to college after several years, there is very little about the college experience that is more intimidating than walking into a classroom full of fellow students that you don't know. Even someone with an outgoing personality, an extrovert, often wonders, "How will I ever find the courage to raise my hand and ask a question?" The solution is to make friends with your classmates--which is not as difficult as it sounds.
Know what kind of student you are, and position yourself accordingly. If this is a class in which you hope to do well, sit at or near the front of the classroom. If you don't particularly care about your grade, sit in the back. Either way, you will be surrounded by students who feel the same way about the class as you do. This gives you something in common besides the fact that you all signed up for the same course.
Observe your classmates to get a sense of who they are and what you might have in common. You might notice someone who seems shy like you or a peer who is reading the same book as you. When you identify a new potential friend, sit near that person if possible.
Smile and introduce yourself. By the end of the semester, you and the person sitting next to you are going to have a lot of shared experiences--you're sitting through the same lectures, you have to write the same papers and take the same tests, and you both know it. After the introduction, ask the other student why he chose this class--is it for his major or for a general university requirement? People love to talk about themselves, so give your neighbor the opportunity to do so.
Participate actively in group activities. Formal or informal class study groups or the ever-dreaded assigned group projects are a great way to make friends with your classmates because you need to meet and communicate with them outside of class time.
Talk to the students sitting near you before class starts. Was there something you didn't quite understand in the assigned reading? Ask the person next to you what he thought of that section. If the people behind you are talking about how hard that last test was, turn around and politely join the conversation. If it's a math class, and the person on the other side of you asks what answer you came up with for problem number 3, compare notes.
Hang around after class instead of rushing out the door for another chance to chat with classmates. Discuss something that just happened in class, what other class you're taking or what you're doing this weekend.
Head to the dining center together after class if it's a meal time. Socializing over a meal is much easier than socializing in class, when you need to focus on the professor and the instruction.
Invite classmates that you enjoy being around to an activity unrelated to class. Are you hosting a game night in your dorm room tomorrow night? Do you need another player on your intramural sports team? Do you have an extra ticket for this weekend's football game? Spending time outside of the classroom helps you move from classmates to friends.