I didn't have one with my first, but it is a brilliant exercise to go through even if it is just for yourself, as It forces you to think about all the what if's and exam what levels of interventions you are comfortable with and on what basis of presentation YOU deem them to be necessary.
My birth plan this time round is mostly more about what I want my MWs TO do and what I DON'T want them to do - little or nothing about me and my actions.. as what I want is natural.. and my actions can be sumed up in just that one word. ;-) However, it is all the if's and buts that I don't want written down.. for all to read, only for me, to remind myself how I feel about interventions. Do you know what I mean? Otherwise it will be Birth plan; natural.. (one line), and then 5 pages of, in the even of me deciding interventions become necessary!
There is a general headings on the NSH choices website for you to think about, but I think that it is a good idea to have a note pad with all the general headings, and then when people talk about the options and their experiences (i.e from birth stories) it can help you examine how you would feel about those presentations - so it becomes something more living.. and more in-line with your wishes. It is really hard to think about from a standing-start.
Sorry that is a semi-unhelpful answer Linzi! ;-)
XxX