Excellent advice, MrDave!!

A few other suggestions I'd add (with some overlap):

1) Do not objectify her hair! Comments like, "Gawd, I love your hair," can be demeaning to your partner. Be appreciative of *her* and what she does with her hair. Praising her hair is great (e.g., "Your hair looks fantastic tonight"), but don't separate it from her and her actions (e.g. "I love f**king your hair" versus "It drives me crazy when you jack me off with / let me cum in / etc. your hair."). You're not just doing things with her hair - you're doing them with her.

2) Show her sites like tlhs.org that have suggestions on hair care, styles, etc.

3) Beware of comments like "how do I make her grow it". You can't make her do anything. You can ask, bargain, and encourage...

My wife has told me many times that one of the main reasons why she keeps it long is because of my constant reassurance to her that she can do whatever she wants to her hair and my encouragement that she actually persues whatever she needs to in order for her to feel beautiful and sexy, including cutting her hair. If she doesn't feel good about it, she's not likely to want to indulge whatever kinks I might have. Keeping her hair long because of my wishes will only go so far.

4) Don't be obsessed with her hair. Another thing my wife tells me as to why she keeps her hair long, is that she knows I get turned on by her, regardless of her hair. I purposely do not ask for hairplay every time we have sex. Do I think about it? Sure. But she needs to know that I can be driven crazy for her, want her so badly that it aches, and be passionate even when she's not triggering my kinks (e.g. when she has her hair in a bun and doesn't tickle).

Anyway, my $0.02....