Choosing a roommate can be very daunting, and involves putting yourself out there (you will probably face rejection, but that's more than okay, as I will explain).
I would like to structure this post by listing ways in which incoming college freshmen might find a roommate - I have ranked these in order of most to least common based on my experience and those of my friends:
Through a college roommate finder
This is a roommate-finding portal offered through your university, that resembles the most basic form of online dating. You will probably be asked to create a profile, and write a few sentences about yourself, and will likely fill out a questionnaire about your habits (when you get up, when you go to sleep, what times you study, how clean you are, etc.).
Then, you will be able to view others' profiles - often an algorithm tells you how their answers matched up to yours. You can message them too! Don't lose hope when someone that looks like a great fit for you does not respond, or has already found someone. If they ignore you, you now know they aren't right as a roommate, and if they have found someone but you get along well, this doesn't mean you can't hang out when you get to campus. Keep looking!
Keep in mind that this feature is only available to students who have already committed to the university. So if you decide super early, there will be less people in the portal, but you might also have people with a similar "early bird" attitude. Also, my university gave students who registered in the portal earlier or committed earlier first choice for rooms, which can be a real benefit of being ahead of the game. Don't let this stress you out though! If you're not sure about a college, it is always better to take your time to make sure you are happy with your decision.
Through a college-centered social media page
This is becoming a popular way to find roommates with large Facebook groups being created for those admitted to a particular college's incoming class. You might find students posting about textbooks and trying to find a roommate, and the benefit here is that you likely have years of social media to look through that will tell you exactly what sort of person they are.
The same general advice as for the roommate finder applies, although keep in mind that finding a roommate means you both will have to create profiles on the roommate finder in the end to match up in the university system.
At a college orientation
I would definitely not plan on doing it this way, as trying to find a roommate at a college orientation can just make your day more stressful than it needs to be. Instead, focus on doing things that will help you get ahead before starting the semester i.e. getting your ID, meeting with a professor you are interested in researching with, ironing out a *perfect* schedule, etc.
However, since universities love creating smaller groups for orientation (10-50 students), you could meet someone that you really click with. You might even talk about being roommates. If you find your soul-roommate this way, go right ahead since this method of finding roommates has created lots of college best friends, including my sister and her current roommate! But beware! It might be worth exchanging numbers first, talking a few more times, and checking their social media before you make such a commitment.
Someone you already know (personally or through someone else)
Although I know many people that do this coming out of high school, I highly advise against this.
The reason I advise against this is that there is a 95% chance (my personal estimate) that college will change you. Having someone from your hometown, high school, or someone connected to your family or friends 'back home' could be a great comfort at first, but will also prevent yourself from getting out there and meeting people. And when you inevitably do so and realize that you are not a part of the same crowd you hung out with in high school, it might become awkward with your roommate.
Instead, if you know someone going to your college, keep their number, and hang out in the first few days of college. This can be a great way to get a larger group together in the dining hall or at a welcome event ("double-date" with both of your roommates, for example). And if you find after a year that you and your friend from back home really would be great roommates, I apologize, but now you won't have to worry about next year!
My own story
I have had two wonderful roommates in my three years living in university housing, of which I shared a dorm room for two years.
I met my first roommate through SIU's roommate finding portal. She was the third person I messaged, and we quickly exchanged phone numbers and texted for a couple weeks before meeting up in person (as we both lived near Chicago, we met up at a mall with our moms). After this meeting, we decided to become roommates and finalized our choice in the portal. We met up another time the summer before college to pick up some furniture at the local IKEA, splitting the items among the two of us. Although she moved off campus after only one year to share an apartment with mutual friends, we are still friends and regularly talk! I think our matching percentage was something around 90% - I realized that I could not talk to her before her morning coffee however, and that she loved to decorate for Halloween - something I tolerated before shouting out "No more pumpkins!" one day, now an inside joke among the two of us.
I met my second roommate through mutual friends at college and we were part of the same scholarship program, so we had met before, although we were not particularly close. We both needed a roommate for sophomore year, however, and we knew that we could both be neat enough for the other. Unlike with my first roommate, we decided to keep our room pretty separated down the middle (my first roommate and I had bunked so as to have room for a couch in the room), but we quickly became very close, so that it was an easy decision to share an apartment in university housing the following year. We chose to have separate rooms , which at that point, I really appreciated (and shared the apartment with two other girls). However, we still made sure to spend time with the other person and had tons of fun - now we talk regularly while I am away studying abroad
I realize that not everyone is lucky to have such a great experience, and is best friends with their roommates after starting out as strangers, but you do not have to become best friends, or even friends, with your college roommate. In fact, being so close to my first roommate resulted in us not speaking for three days when our friend group fell into some bad drama, that has since been resolved, as we are much older and mature now. So focus on finding someone that is the right level of tidy for you and that will have respect for your personal space and stuff!