How to flirt with a guy...

I have a thing for this guy which I met this year.We see each other every day and we say hello to each toher.We're both on highschool,but in different classes.
I'm really not sure if he's interested in me or not,because sometimes it looks like he's interested and other times it looks like he's not.
Sometimes it looks like he avoids looking at me,other times I catch him staring at me very often,when I'm not looking.
What I'd appreciate is if you could give me some tips on how to improve my relatioship with him,like how to flirt with him.I already have his phone number and he has mine.At thursady we have classes in rooms next to each other,so I think this would be a nice opportunity for me to flirt with him,I just don't know how to start flirting....
Any advice is welcomed!

sounds like you do like this guy quite alot.Flirting counts as something as little as just smiling his way or holding eye contact,its enough to give him the idea you like him.also if you have his number why not text him a cute short little text saying something like 'it makes me smile when i see you'

Yeah I already thought on text messaging him,but unfortunately I lack ideas on how to also flirt with him by sms.Any more ideas on how to flirt with him?
Thanks ina dvance for the help!

Make him think about you as you part. Say 'hi' or 'bye' or something unimportant as you are holding his arm, thats sure to leave him stunned.