There's lots of different types of flirting. There's the "giggly-oh-look-how-cute-I-am" kind, the subtle body movements/touching kind, biting your lip kind.... however biting your lip without looking constipated is kinda hard...
I usually go for the 'giggly' one, though that's mostly because I'm a hyper/bouncy person by default. If you're not the cute girly bouncy kind then it would be sort of awkward for you to just start. Leaning in when you're talking is always good, if you're at school or work then wait until you go to the cafeteria/lunch, and try leaning against them (subtly). Brushing your arm against there's is another good way to go. Lower your voice when you lean in and stare directly into his eyes, making it seem like he's the only interesting thing in the room, and act like you're sharing secrets (though don't make it obvious)
There's other things, but I can't fit them all in.
My friend has the same probable just be your self and stay happy and laugh a little enjoy the special conversion between you and him I may have to ask this same question and have fun and talk to him and smile
Come up to him and say: "Is that a roll of silver dollars in your pocket or are you happy to see me?" If you really want to make his day, substitute "Louisville Slugger" for "silver dollars". If either of your responses to this suggestion is "Huh?" then you may not be meant for each other. Cleavage helps a lot. So does thigh. I usually get those types of signs flashed at me, but mostly the signs I get is the gal calls a priest who starts sprinkling holy water on me and shouts: "The power of Christ compels you to exit this body now!" (I'm not sure if this is caused by my comb-over or my breath.)