In some places there are standards, like it's at some specific height or whatever. But a lot of it is just a matter of looking around. There's a lot of braille that is (imo) theatre, appearing to do something useful more than doing something useful. For example lately there have been calls in a region of Spain to mark garbage containers with braille, by a political party, resulting in many blind people wondering if they're going to install fountains by them to wash one's hands after the search.

You just feel for it. There's no magic trick.

Braille is most useful on buildings full of nearly identical rooms. For example, school/university buildings. If the braille is placed in the same spot on every door, I can easily tell that I went the right way, and am entering room 307 not room 301. Plus, in the case of washrooms, it's worth taking a moment to feel around for the Braille, rather than risk entering the wrong washroom. I agree there is a lot of Braille theatre though. One memorable time, a friend pointed out to me a sign that had braille on it. Unfortunately, the sign itself was above head height! I would've needed to stand on a chair to read it. We were both quite amused; no idea what thought process, if any, went into putting Braille there.