It's Not Always That They Like
I see so many questions on here, people asking "does he/she like me? I saw them look at me, they smiled and then when I looked back I saw that they looked at me again, WHAT DOES IT MEAN??"
Now, for the most part if you're being looked at, rather than zoned out at, there's something about you or you that day, that's noticeable and caught their attention. Maybe you look cute, maybe they're trying to read your shirt, maybe there's something on your face.. but JUST BECAUSE you see someone look at you does not mean that they're interested in you, and there are a plethora of reasons why else someone could be looking at you instead.
From my perspective, if I catch someone looking at me and I'm in a good mood I might just smile as a greeting, but then just carry on with my day and think nothing more of it. Other times, maybe I caught you looking and I think "why's this person looking at me?" and shrug it off, BUT THEN I KNOW YOU'VE ALREADY LOOKED AT ME, so I'll very likely look up again to see whether or not you're still looking at me. And if you are, that'll perpetuate the cycle even more and I'll look at you AGAIN to see if you're STILL looking at me, and each of these times if I see you doing so, I'm going to look away. Not because I'm super into you and trying to be coy, but because now I'm like "this is weird and awkward, person keeps looking at me and I keep catching them looking at me.. but I want to know if they're still looking at me and why.."
Now, don't lose hope friends, like I said, there is likely something about you that caught their eye in the first place. But so many want to believe that this means something, and you'll have people hype you up saying that it does. Calm down, take a step back and don't think too much. If you catch a smile your way, return it, and at the end of whatever it is you're doing whether it's in class or work or an event, you can use that as an opening to walk up and be like "hey I just wanted to say I really like your __________". Boom.