Yeah! I personally struggled with that a lot with all my relationships because I wanted people to see me a certain way. New people were rare to come by for me so I think I put a lot of pressure on myself to "succeed" or have it go the way I thought I wanted it to, and it made me upset with myself when it didn't. It's different for everyone, but I think the best mindset you can have is to be okay with it not working out at all! And that's just fine, because sometimes the best thing you can do for someone else is leave them be if they aren't responding. Just meeting a new person once can be satisfying enough on its own if you let it. Being offered someone else's time really is a gift. If that's where you ground your expectations, anything else is a pleasant surprise :)

As for the "wrong ideas" thing, it sounds to me like they're saying you shouldn't make the other person think you want a relationship when you don't, or vice-versa, but maybe that's getting ahead of things. If we distill that notion to its essence though, we end up at the importance of being a good communicator -- can you convey to the other person what you think and how you feel. That take lots of practice. If you ever get into a situation where you think you did or said something wrong or awkward, just say, " Whoops, I'm not the best communicator, still working on it!" and either try again or move on. That kind of show of vulnerability can help make who you're talking to feel more comfortable.

Sorry for the wall of text, but I'll try to leave you with this mental image to help let go of expectations: I think of it like tubing down a river where sometimes you bump into other people doing the same and have a chat. Enjoy it while you're floating alongside each other, because the current can change unexpectedly or something can pull them away at any time, and trying to predict or change that is like trying to fight the current. It's impossible and you'll look really silly trying to. So just go with the flow, man.