I find this difficult as well and often thought if I didn't bring up big stuff then it was a wasted session.
So I started noting and listing themes I wanted to mention it held my self accountable and often meant I would bring them up at the beginning of the session because I had already intellectually prepared for it. Part of being able to bring it up is emotionally detach from the issue until it's raised in session. I find these sessions are better and I leave more grounded. The ones I don't prepare or go too far in are often the ones I haven't prepared go in defensive because I feel things are less expected and then end up sharing things I have not processed at all and way out of my window of tolerance.
My mine advice would be to have an imaginary session with in your head to start to feel what you want to bring up.