For me, I guess there are a few things I could say are 'vital'. The first is establishing a good client/therapist relationship, becoming known to the client enough that they can begin to trust you, but not over-stepping the mark and letting them into your world too much that it enhances transference issues. I think this is very tricky.
As many people have said, 'silence' kind of goes with PTSD and therapy and I think you need to be prepared for that. Many therapists are taught to just sit in silence and wait. My first therapist was smart enough to see that that wasn't going to work - that I just 'couldn't' talk - ,my anxiety was that great that it inhibited my ability to think about what I was going to say, let alone get it out and trust someone with it. In the beginning, he would get me to write things down and email them to him, so then he knew what to ask me, explain to me or reassure me about when the session started because he knew I wouldn't be able to get the words out. Then he slowly transitioned me into talking. If I was stuck, he would leave it for a while to see if I could get it out, then he'd reassure me, help me or move on and come back to it. My favourite line I always remember him saying is, 'just say the simple, honest, dumb stuff that comes into your head'.
For me, I was diagnosed with PTSD and DID. Some therapists do not believe in DID. This is not helpful and makes those who actually have it feel crazier, more worried than they actually already are. I used to be paranoid when I heard things like that, thinking to myself, 'Oh crap, what if I'm just so unhinged I've somehow made all this up?!'
I think sometimes with PTSD and especially DID patients, you have to be understanding, but also quite firm on boundaries. We're, or at least I was, very damaged. We'll over-step the mark a million times given the chance. Make the boundaries clear, remind us when we overstep it, but show compassion and even better, educate us about WHY we are overstepping the mark - what is the root cause that makes us do this?
If we have other people who are good for us in our lives, encourage us to lean on them to, not just on you, because ultimately that's where our life lies outside of the therapy room and we need to progress ourselves towards it as we become stronger.
Encourage us to be getting out and doing something. Some of us with PTSD can't work - I know I couldn't in the first couple of years of flashbacks, when I was really bad. But doing volunteer work, going out and seeing a friend for a drink or a walk - these simple things kept my life going, kept me grounded and when I was really bad, although I didn't feel like seeing anyone, it would distract me at times. In fact, the days when I didn't go out and there was no one around, I could guarantee were my worst days.
Don't offer vague encouragement if you can help it, like, 'it will get better one day' or 'things get better when you're older'. I used to hate that. I want the concrete. What can I do NOW, because the future, when you're going through something so intensely horrible, seems so far away.
And lastly, I would say, take care of yourself and have a good work-life balance. I know nobody is perfect, but if you are stressed or not looking after yourself, you won't be on the top of your game in therapy. And I feel like this is a horrible thing to say, but I find trusting a therapist who seems obese or not 'together' a bit like trusting a skinny chef or a very ill doctor. I can't help it. I think, 'well, how are they going to help me if they can't help themselves?'
Good luck with your work. Thanks for coming on here and thinking beyond the textbook, because of course there are similarities in everyone's stories, but every story is unique and requires unique perspective.