What saratustra said is right, you could have an ideal in mind but by the time you get to 35 weeks you could have pressing medical reasons to think again, so try not to get too wedded to a certain way of doing things at this point.
Not everyone rates the antenatal classes offered by the nhs but I found them useful in helping me work up a birth plan, and so I would say it's worth waiting until you go to those before you make any major decisions. My plan isn't so much a 'my birth should go like this and not deviate' kind of document. It's more a list of what is and isn't a priority for me. So for me major priorities include, having my DP as birth partner, skin to skin contact straight away, water birth/active birth if possible. Not so important, I don't have a strong feeling on pain relief, I'll take it if I need it, I'm not planning to be a martyr and I'm not ruling anything out. And my plan makes it very clear that if medical advice goes against what's in the plan I'll discuss with the doctor/midwife and consider all options, again not ruling most things out (except forceps, they give me the absolute horrors).
The antenatal classes going over the various interventions and how they all worked were really useful in helping me think about how I felt about what could happen if things go wrong, and where my priorities would lie. I also talked it through with my DP, did he feel comfortable cutting the cord, doing skin to skin with him too, what would happen if for some reason I had to have a c section under general anasthetic, etc, so that his thoughts were included too.
The NHS has a handy dandy page which walks you through the kinds of things you might want to think about as well:
www.nhs.uk/conditions/pregnancy-and-baby/pages/birth-plan.aspx
It's early days for you so you have plenty of time to research, and ask your midwife loads of questions. I would also recommend taking a tour of the places you're thinking of giving birth too, as that may influence your birth plan. Hypnobirthing comes with a lot of recommendations as does mindfulness, they're quite similar thinking really, so you might want to look into those before you decide as well.