He will try to spend time with her.
... And try to get her attention.
The guy will tend to not talk to the girl not that much but try to talk to her as well. He will be shy around her and clumsy or distracted.
flirrrttt. laughhhh. makeee jokeeesss. high-5 too often. tease herrrr. omg almost everything.
He might laugh at all your jokes, look at you, joke around you, talk about you.
You know when he is flirting with them talking to them a lot. Being too kind to them. Make u laugh. Try to get to be friends. Those stuff basically.