Actually, I'm willing to say that my past experiences with a person, and how many opinions we share, really says more to me about how much they understand me than anything. But if it's caring I'm looking for, most often very little it required to show me they're listening and caring.
If someone is uncomfortable hugging me or touching me, I don't want them to do it anyway, haha. Although the results could be humorous. "Hey, why do you have that funny look on your face? Hahaha!"
When I'm physically demonstrative, it's not planned much at all. It's so circumstantial. I think you're either comfortable doing it or not, and you either have a good eye for opportunity or you don't.
I think part of what's endearing about physical affection is that it takes a bit more, how shall I say, effort and confidence, to be physically affectionate.
My best friend is INTJ and female. I'm INFP and female. We get along pretty great. We're almost always on the same wavelength, and we share most of our woes, and we're just really very comfortable with each other. I know she has similar pain to my own, so that really bridges most gaps.
More recently I've become more comfortable being physically affectionate with both her and her boyfriend (an INFP male, and my next-closest friend). Hugs, touches, they all come naturally to me nowadays. I just go with the flow. I like when someone is physically affectionate toward me, I really do, so I think for my two closest friends the same is probably true. If not, what's a few more hugs going to mean to them anyway?
I think physical affection, for me, is especially indicative of confidence and self-esteem. For most of my life, being hugged or physically affectionated (hehe, I like to turn nouns into verbs, it's easier that way) was extremely awkward and uncomfortable. I'd sitffen up. I didn't know how to respond, and I thought perhaps reciprocation was in order, but now that I'm older and wiser and more experienced, I go, "Pshaw!" at that notion. More often when I'm physically affectioned, I don't return the affection at that time. I just let it happen and enjoy it, and keep it in mind to repay them later.
Oh, but this thread is about comforting another female with physical affection. Hmm. My best friend, probably due to her inferior Se, has a lot of anxiety attacks. She's told me many times that during these panic attacks, in her mind she really feels this is the end of her life, her last day on earth. I've never experienced anything quite like that. But she knows I care and that even if I haven't had the exact same experience, I'm as familiar with anxiety and fear as anyone, and I want her to be happy and have peace of mind. Physical affection aside, knowing that is enough.
When she's crying during one of these attacks, usually her boyfriend is there to comfort her and hold her. For me, it's extremely off-putting and unsettling to see her in such a frenzied state of fear and sorrow, and I don't even know what to do for her. So far, it's only happened once while I was in her presence. I just hung around and waited for the pain to pass. I don't know if one day I will comfort her physically, but it may come. If it did, I'd probably give her a lot of little hugs and touches, spaced out a bit. They'd be pretty spontaneous and pretty brief. I don't think they'd last for more than a couple minutes, tops. Lol. *is imagining this*
But yeah, others have given good insight. If you're not pretty loose and comfortable doing it, you don't HAVE to. What's it going to matter anyway? True friends know you care whether you're physical about it or not. When you develop a bit of an eye for seeing the opportunity, and when you're comfortable taking that opportunity, just do it. Like the person above me said, it's the feeling behind it that counts, so probably any action you take, physical or not, will mean a lot to them in times of need.
Haha, and even if the hug looks completely retarded, elbows bumping, boobs getting in the way, etc, to your friend, it will mean a lot. =) I'd be spontaneous! See what you can come up with in the moment, lol.