How to read your Opponents Mind when playing chess?

1...f5 is terrible, better is any normal move.
2...d6 is terrible.
5.g7 wins a rook.
7.Qa4+ is bad, forcing the opponent to develop.
8...Bc6, better is developing with 8...Nc6. The b7 pawn isn't so important, plus white only has the queen developed so something like 9.Qxb7 Rb8 shouldn't worry black.
9.Bc4, I understand this was probably on purpose because you get to play a few checks, but I don't like it because it unnecessarily give up material. 9.Nc3 is fine.
10...Kd7 may be ok, but it's really risky. Obviously safer is 10...Kf8
11.Qe6 is not a good looking move, taking your bishop out of the attack. Engine confirms Be6 was better.
12...Bxh1 is of course bad. Black inexplicably isn't worried about his king on the 3rd rank with no pawn protection.
It's easier to know what people are thinking in blitz because pauses there are more meaningful, and especially when they're lower rated it's sometimes easy to know what they're thinking.
Basically, the better you are, the more comfortable you are with tension and the strategic ideas in the position. So in games where neither player screwed up their opening, the lower rated player generally starts feeling uncomfortable first, and usually tries to go for some simplification like trades... if not, and they try to tough it out, you can sometimes tell that too because they'll keep the tension in bad ways.
When there are definite threats, that can make it easy too. For example after a few quick moves they stop to think, so you realize they notice the threat. If they keep thinking, you know they're calculating certain lines and realizing certain obvious moves aren't attractive. If they're much worse then you, sometimes you can get a really good idea of exactly which defense they'll try... especially if you've played them a lot.
Sometimes in blitz, I'll even say "now my opponent will think for 30 seconds, and play this bad move anyway." Of course sometimes I'm wrong... but sometimes I'm exactly right
Once I watched a guy (who I had played a lot) think over his defensive move. I knew exactly what he wanted to play, and I knew he was calculating that it failed over and over. I knew he was then looking for alternatives... but the alternatives made the position messy (which I knew he didn't like). So as he thought even longer, I knew he was going back and calculating the move he wanted to play over and over, seeing that it was bad over and over again haha. Finally he played the move that was basically forced from the beginning, but it was so out of his normal style of play that he agonized over it for a long time.