Flirting
Alright I'll give it a try. Although I've been out of the dating pool for awhile, I'll give advice and examples I have used and that I would feel comfortable using.
Flirting is all about body language. Now just to make it confusing the language changes when you are dealing with persons unknown to you, co-workers/classmates, and where you are.
Are you looking to get the attention of a guy across the room? Make eye contact, hold it for a moment, and then look down and away and resume conversation with whomever you are with. Repeat a couple times, if the guy doesn't come over and try to start up a conversation he is either shy, or not interested. Although if he is meeting your eyes more than once there is some interest there. Look for a way to get closer to him? Is he sitting near the ladies room...freshen up! Don't forget to smile as you pass by! Near the bar? Get yourself another drink as close as you can, if its a smaller establishment ask the bartender to send a refill to your interest. Sports fan? If he's wearing something sports related, and you have a similar interest (mine is football) make a comment to strike up a conversation.
Got a crush on a co-worker/classmate? Go out of your way to make small talk. Notice their presence (even just a nod can make someone a bit happier that they've been noticed), and acknowledge when they leave ('See you later' if they were in your group, or a big smile if they aren't close enough for a verbal cue). Ask for opinions/help with something. Guys like to feel useful. Ask for a small favor, "Oh are you going to refill your cup of coffee? Could you please bring me back a cup too?" (that ploy also works at concerts, especially when you don't want to lose your spot) If you spot an oppurtunity to be helpful, he/she needs a ride home, help setting up a presentation, a hand with their things etc, take it! Especially grab the oppurtunity anytime you can get to socialize away from the workplace.
Although its hard for an infj to make a first step, there are little things you can do to make yourself seem more open if you aren't comfortable doing anything too overt. If you are talking to someone, turn your shoulders towards them...face them completely and lean forward slightly. The posture indicates you are interested in what they have to say, and for most guys may indicate you are interested in them as well as giving them a courage boost. For all the bluster, a lot of guys are very fearful of rejection, and will prefer not to make a move rather than to risk getting hurt.
ETA: Oops, I guess as an ntj her comfort levels wouldn't necessarily be the same as an nfj.....maybe i should have looked at that mbti part...