talk to them normally, ask questions, share stories
pretty much holding a long conversation while having fun at the same time is concidered flirting (and you won't even know it)
you won't know it, but flirting does happen
just be friendly!
"Love is patient, love is kind. It does not envy, it does not boast, it is not proud.
It is not rude, it is not self-seeking, it is not easily angered, it keeps no record of wrongs.
Love does not delight in evil but rejoices with the truth.
It always protects, always trusts, always hopes, always perseveres.
Love never fails. "
-1 Corinthians 13:4-8