I try very hard to make sure that at least once per week I do something *totally and completely* for me. Something which does nothing for anyone else.
One thing I try to do is give myself 30 minutes around dinner time of "no responsibilities". This means that for half an hour per day, I 'schedule' time to not feel guilty about doing something for me. I put the puppy in his crate if I have to, and I eat dinner. Sometimes I read the paper or a book while I"m doing it. I note the time so I know how much longer I have of "me" time. Some nights the stars align just right and I can take a whole evening of me time - but most of the time not. In either case I get my 30 minutes without obligations (I also don't answer the phone during this time).
The past two weeks my "me" activity has been reading a series of books I've wanted to read. I give myself half a day somewhere during the week to just read for me. Sometimes my "just for me" is watching movies or tv shows. During my "me" time, no one else is allowed to be part of it. It's my chance to sit inside my own skin. Sometimes I just sit and stare off into space or take a hot bath or sit by a fire. Whatever it is, it isn't for anyone else's benefit but my own.
This time reminds me that I am just as important as everyone else and everything else on my list of 'to do's.