There's this thing called platonic love at which, I have found, INFJs particularly excel.
That said—one way to my INFJ's heart is through her stomach. She's very skilled at identifying and pointing out the ways I've tailored the dish especially for her. MBTI theory would not seem fit to describe how to love someone. There are so many ways to show love.
The best way is also the most obvious: find some way to express your sentiments, then observe the reaction. It's a gradual process, but the most accurate. Try different things. See which things elicit the strongest positive reactions.