I'm not an ISTP, but close enough I guess lol.
I personally would want you to do little things. Vacuum, do dishes, housework, cutting the grass, getting groceries (without me) etc. That might sound sexist, and I don't EXPECT you to do it, but just doing extra little things turns me on. Like if I came home and my bed was made and the bathroom cleaned, ooooh, I would freak out (in a good way). But realistically, maybe filling up my car with gas or something? Hm, you get the idea, I can't think of any non stereotypical things atm (unfortunately XD)
Also, in regards to what turns me on, not necessarily showing ME love, but getting me on is when I see a woman do something motherly. I work at a waterpark, and there was this lost little boy and one of the girls I work with went out and helped him and carried him (he was like 4) omg I freaked out in my pants.
Obviously this is all very "traditional" type stuff, and in no way do I want a "traditional" wife/girlfriend, but when you pepper those types of things into a regular modern relationship it helps a lot (imo).