So what does it mean to trust your reader?
For me, it meant not repeating the stuff that was important for the reader to know. I'd try to be subtle but clear. Then a page later, I'd say it another way. Then again, a few pages further along. My critique group was ready to beat me over the head with my own manuscript, and I can't count the times I heard, "Yeah, we got it the first time."
So trusting your reader means you don't beat them repeatedly over the head with stuff.
But it also means you don't give them every little nuance you're writing about. Your readers have life experience, and I'll just bet most of them have been in love and been disappointed by love which, if you're writing a romance, means that at one time or another they've felt everything your characters are feeling. They have that experience to tap into, so writers don't have to give them every tiny detail of what the characters are feeling. In fact, if you do all the work for them and don't let them bring anything of their own to the table, the reader will have exactly zero emotional investment in your story
The flip side of trusting your reader is learning to trust yourself and your ability to convey what you intend to. Yeah, I know. For some of us, this is just as tough as learning to trust the reader. But this is another place where critique groups are helpful. If you pare down your explanations and no one says "Huh?", pare it down some more. When your critique buddies finally start saying, "I don't get it" you've gone too far. You'll be surprised at how little you need to explain and your writing will get tight, lean, and effective.