Big things for me to include are strong preferences for where/how/what people do controllable things. For instance, I canNOT stand to have anyone eating in the same room with me, particularly during labor. So no food/gum/etc. in my birthing space, at a minimum. If I'll want specific foods or drinks, I may put that down. I definitely worry about my birth team and taking care of them, so I have previously put info for them on what is available to eat and drink, how to find things, etc. I have specified desires that I might forget, like having an herbal bath with baby and when I'd like that to happen.
I definitely agree that it's best to avoid (in a home birth setting) too many details on how you want things to go; too many are uncontrollable! Having basic agreements/understandings with your care provider go a long way to what you would be making a birth plan for in a hospital. I do tell them NO suction, no cord treatment, etc., which are things that may vary from MW to MW and family to family.
Oh, and I absolutely have to make sure that everyone knows I MUST have my kids called in when we're anything like close to birthing. They've ended up missing the last two births because the end came too fast and they were less than a mile away at my parents' house. This time, they've declared they will NOT leave.
I thought having moved 8 miles away would mean they wouldn't even have the opportunity to leave, but now my parents are moving closer, under 5 minutes from us. So we will all have to stick to the rule of having them in/around the house but NOT further than that! 'Cause I'm not going to have another "do over" opportunity - ever!