Let's not mince our words. You are sleeping with his daughter. That should frame this entire lesson in the required context - your relationship with the father of the woman you love will be the single most awkward in your life. You have just one thing in common: a desire not to anger his daughter. That is all. Despite this lack of shared ground you have to get on. Unfortunately this is statistically unlikely. You're of different generations, beliefs and interests. Regardless, you must try. You really have no other choice.
SOME COMMON MISTAKES
Let factual inaccuracies lie
The worst thing you can do is be a pedant. If he lays claim to having served in Vietnam and giving Sir James Dyson the idea for his revolutionary vacuum cleaner, let him believe it. To try and shoot him down is to crash your own plane into the sea while taking aim.
Know where your partner's loyalties lie
She might be in love with you, but that man over there, the one suggesting that you have the upper body of an eight-year-old Russian gymnast just because you've never played rugby sevens, is her father. She won't be impressed if you point out that he's an idiot, even if you are right.
His overbearing, try-hard alpha-male posing might be annoying, or his powerfully boring talk of accounting methods might be tedious. But remember, one day your daughter will bring a man home. And if you're not boring by then, you'll certainly want to believe you can beat him in an arm wrestle.