A birth plan is an outline of how you would like things to go during your baby's birth, including your preferences on pain relief, positions in labor, and your thoughts on interventions, such as the use of forceps or ventouse. But do remember, the plan it is not set in stone, and you can change your mind about anything - at any time - before or during labor.
A birth plan is a useful guide for the midwives helping you with your birth, and also for your birth partner, as they will probably be the person speaking to the midwives and doctors on your behalf, and keeping you focused as your baby is born.
Before writing your birth plan
Before you write your plan, talk to your friends who have recently had babies, and ask what they had in theirs, and what they might have worded or planned for differently.
You could also join a local antenatal class and chat to other moms who've made a birth plan and been through it before.
Doing your research on the various types of pain relief and facilities offered by your hospital is also really important (there's no point in writing that you want a water birth if the hospital you will be using has no tub or birth pool on offer!).