Here's what you do - you figure out where your crush usually sits, get to class early and sit in the seat NEXT to that. Then you casually put one leg up on the chair you're hoping they sit in to dissuade any non-crushes from sitting there.
When they end up sitting in a random seat on the other side of the room, sigh with defeat and fantasize about them secretly just being too in love with you and sitting on the other side of the room because they get nervous around you and your irresistible sexual aura.
Make sure to also tip an awkward amount, like three $1 bills. Like, that's not a normal amount to tip for coffee AND your crush-barista turned around to get your coffee when you put it in so they didn't even see it.
When you get your cup, check to see if they did something like this:
New picture of them at the beach? Like it! Post about a recent news event? Like it! Sharing a Facebook video of a stolen Vine of SpongeBob? Like it AND add a comment with the "crying laughing" emoji. They'll definitely note how attentive you are and want to have sex with you.
Every time you see them, you say "Sup, J-Dawg?" even though no one else calls them that and they definitely don't have a nickname for you. Also their name doesn't even start with a J but you're in too deep now so you've probably just gotta commit to it.
They into Bernie Sanders? You share every Young Turks video you can find. They into Game of Thrones? You're posting about the latest episode and fan theories about how Sansa is DEFINITELY pregnant with Ramsay's child non-stop. They like The Big Bang Theory? ...well, suck it up and post "Bazinga!" or whatever.
Maybe, someday, they'll like one of your posts and that's technically getting to second base in internet relationship terms.
Maybe it's time to admit you don't know how to flirt. People who know how to flirt don't click on internet articles about flirting techniques.
Honestly, this is the most popular technique out there, so there must be SOMETHING to it, right?