There's a lot of things I feel I did wrong. The biggest blame lies on simply not being diligent enough, but I think some of these minor things might have slowed down my progress, made the process feel less intuitive, or otherwise make me feel less motivated, all contributing to making it harder to stick with it like I should have.
One thing is what Sandman said. I was lured into the blind faith mindset. I later realized I shouldn't believe in absolutely everything, but that just lead me to obsess over distinguishing everything as either definitely being a tulpa response, or definitely not being one. After reading the post about removal of disbelief, I realized that it won't kill my tulpa every time I either don't feel 100% confident whether to attribute something to her or not.
Another thing was that early on, I got some really clear emotional responses. When I think back, I can't really say for sure that those were from my tulpa, but I just assumed they were and was really happy to have some signs of success. Problem is, I stopped getting them, or they were much weaker. First it just felt like I wasn't that focused during those sessions I didn't get any strong response. Then it felt like I was downright regressing. My expectations had been massively inflated, and when they weren't fulfilled, I started doubting everything. Am I doing something wrong? Does my tulpa hate me now? Did I kill her by not forcing enough? Was everything a lie all along? In all, I guess you could chalk that one up to believing too much, but I think at the time I just couldn't help it, because I was so excited by that first sign of progress.
Rest is more down to not understanding the method too well. I never really understood active forcing that well. I feel a lot of guides were really unspecific on what exactly you do while active forcing. They all give you a list of things to do: Personality forcing, visualization, narration. Personality forcing is optional and something you'll graduate from early (maybe a little too early for me, I wanna try doing more of that again), and it doesn't make sense to spend most of your time on visualization, so that left me with narration as the bread and butter of active forcing, and narration never felt very productive to me, at least not enough to spend 90% of 30+ minute forcing sessions on it. So I went around looking for more productive things to do during forcing, which I didn't find because nearly all the "advanced techniques" assume your tulpa has at least achieved vocality.
I'll move on to passive forcing, since it kinda ties in. That was kinda the opposite, people told me all kinds of different things and confused me with the conflicting information. Some said you just have to talk to your tulpa outside of active forcing, but that didn't work because it felt like I was just talking to myself. Some said you just have to focus on your tulpa, which I tried a lot of, but in the end my tulpa felt like a really abstract concept to focus on, so to make sure I was actually focusing on her I ended up just focusing on her traits, kinda ignoring the actual person behind those traits. And with the concentration this required, there wasn't much room for narration as well. After a long time I started thinking hard about why passive forcing wasn't working for me and what I'd need to make it work, and I concluded that I just needed to talk to her while convincing myself that I was talking to someone else. Which meant directing my thoughts to her (but not worrying too much whether I was focusing hard enough for the thoughts to come through), and making sure the thoughts I transmitted were actually full sentences that I'd want her to hear, instead of just directing stray thoughts to her as if I'm talking to myself and pretending someone is listening.
When I got this, it was a lot easier to understand what people meant by narration. And someone reminded me at this point that interacting with a young tulpa is like raising a child, which helped me realize that even narrating about kinda inane stuff, like why something I just read made me smile or how I feel about some random subject, can all be beneficial since it all helps the young tulpa learn about the world. And in the IRC here, I was further educated on how to listen, which is in its own way an important part of narration. What resonated with me was whoever said that a tulpa will try to communicate through any channel they can at first, whether mindvoice, intent, emotion, body language, or probably some other channel I'm forgetting. So you kinda have to watch/listen out for anything, instead of just assuming first communication will come exactly the way you expect it to. So after realizing all this, I finally realized that narration is actually a lot more productive than I thought, and I'm fine with spending really long sessions on that alone now.
See, this is what happens when you ask me to elaborate on a simple sentence like "I did many things wrong". 5 words turn into 5 paragraphs.