Try waiting for a very casual moment when you're both very comfortable, perhaps when you're sharing one of your favorite activities. Put your hand on his/her shoulder, or forearm, or hand. Just a quick touch. Observe the response. If it's positive, then by all means press your advantage. If it's negative, then keep your friend--don't push it.
Note that this is just the straight answer to "how do you flirt?" If you really want to become romantically involved with your best friend, and he/she really is your best friend, then you guys are already talking and sharing lots of emotional intimacy, so I would highly recommend that you just be honest and express your feelings. If you get a positive response, then flirt like crazy, and I bet you won't need any advice on how to do it.
He'd say it
i have no idea izzy!
see if he is flirting it is easy to see
well first if your a girl it will be easierif you where flirting then its a diffrent story anyway just go up to them and say sorry i looked like i was flirting with your man/woman but i wasint anyway im sorry please forgive me
can't hurt to ask
Tell them noob
This can mean only one thing: love is in bloom.
First find out if that's the actual circumstances. If your best friend is flirting with you, he's being a little overly "friendly" and should have some respect for who you've chosen.
She is always arguing with him and talking with him and they are really close
Look at it the other way around. If he was with you but flirting with your friend. You should probably tell your friend.
A friend who is flirting with all the guys may be insecure. Your friend may crave attention and feel that flirting with everyone is the only way to get it.
You are in a tough situation. I say tell your best friend you like him too, and if she knows, then let her date him. If by her unlucky chance they break up, ask her if you can go out with him. Hope i helped =D