1. You are an INTP male, like myself.
2. You are attracted by the opposite sex (yes, I am being heteronormative).
3. You are fascinated by female INFPs especially.
4. You would like to have more things to talk about or amuse INFPs with.
5. You have some things that have worked in the past with said female INFPs.
Yeah, INFPs seem to love "asofterworld". Something about the dark emotion, the passive aggressiveness, the photos that just barely correlate to the words. I mean, I love it to- but I was introduced to it by an INFP. If you meet an INFP who hasn't heard of it... link them!
Talk about spirituality. Shouldn't be hard to do, but the problem is that many of us INTPs are firmly set in our ways. We have our opinions about religion/spirituality... but you'll do best if you're able to have a more flexible point of view to discuss these kinds of things with her. She'll probably appreciate your interest in hearing her own beliefs (which will not be mainstream).
Funny/absurd hypothetical situations... humor! Things like "oh man, I wish I had slashed the cook's tires; they ran out of vegetarian food today!" Over the top things. Maybe a little but cruel or principle-based. Expect a playful objection "Nooooo", and play on!
Be wary of board games. INFPs like them, but they like them because of the social interaction, not because of the empire-building.