It starts with honesty,
Honesty? Like as in being honest and direct with what you feel? Or tell her that today you saw some good porn and you spend the next 40 minutes masturbating to it. Lol
vulnerability,
I think I showed my vulnerable side to her and it freaked her out. I showed her that I am self conscious, unmotivated and controlled by fears and myths.
and being a non judgemental listener.
I think I never judged anything she said. But I did judge a lot in what she didn't say, what she portrayed but didn't verbally said.
Don't hold stuff back -- even if you think your feelings are "stupid", explain them.
Honestly, it's the little comments she made after I said "oh, last night I watched 4 hours worth of anime". Then she'd make a remark about me being obsessed with anime or something. Nothing too big but I'm self conscious as it is with watching stuff like that and i feel people judge me for it. It's not because I didn't want to tell her, it's because I was afraid she would think less of me or make fun of me.
Then we'd argue about not being open with each other, I tell her this exact thing and she'd say she didn't judge me. But then I say, "you don't make it any easier, I feel either you just don't care what I like and disregard what I tell you or you'd make witty remarks about it. Make me feel you judge me for it."
It helps your partner understand you and builds trust. Also, maybe reminding people that you will always listen to them without judgement will make it easier to talk about things that are uncomfortable.
I think, and I even suggested this, when someone tells you something, even if you have no clue what they are talking about. Just continue asking questions about it, make it sound like you would like to know about it and why they're interested. It engages you and your partner, makes your partner feel like he's being listened to and you respect his hobbies. Even if in reality you don't give two shits about it. But giving that sense of "oh she's listening to me and understand me!" Is a nice feeling.