Ari, it may not be that you don't know how to take care of "one's self," but more that you don't know how to apply those ideas to yourself. There's a big difference, and knowing which camp you fall into tells you how to proceed to change things.
Here's how you can see where you fit: think about someone you know- a friend, a niece, a child... anyone, really, although I find this more useful when people envision someone they care about. Now, once you've got this person's image in mind, ask yourself what that person needs in order to feel/be taken care of. You can think of it in two ways- what he/she needs on a daily basis and/or what she needs right this second to be taken care of.
If you quickly come up with things she may need, especially if these things seem obvious to you, it shows that you do have a theoretical idea of what people need in order to be taken care of. If you draw a blank, can't think of anything she might need or how to get it for her, you likely fall into the camp of not knowing what a person needs, why they might need it, or how they could get it.
There are ways to resolve either of these situations.
My experience is that people who suffer from eating disorders mostly fall into the first camp. When I ask someone to visualize another person, she can virtually always (and instantly, usually) come up with all kinds of things she would do to take care of this person. It seems obvious to her, like "duh, of course this person needs this!"
But then I ask why those same things the imagined person needs wouldn't hold true for my client also, and she draws a blank. She gets the idea theoretically, for anyone else. Just not for herself. So, there's the work- helping her figure out how she can apply all this to herself, and why she hasn't been able to so far.
It's important you don't get these two states confused. If you do, you could spend lots of time and energy working on the wrong issue- and end up very frustrated and not getting anywhere. Who needs that?! And I've seen it happen often, because it can easily look like people who have eating disorders don't know how to take care of themselves. It's a lot like that disorder itself- it looks like it's all about food and weight, when really it's about so much else.