I don't think you can be 100% accurate at a live game, it would all be estimation, but if put him on a range of
hands base on the board, u then work out ur equity base on the outs u have to improve. If u have him on a range and you're facing a bet, you can then weigh ur equity against the pot
odds, if you're equity surpasses ur
pot odds then it's a +ev decision to call, however if it's a situation where his range + the texture board crushes u then follow ur gut. But for me it depends on so much variables regarding the player. But yh work out ur equity base on ur outs to improve then compare it to the range of hands u think he would play, then let pot odds, position etc inform you further to make a final decision. Feels like I rambled but hope something I said will be of use