It is all about looking at the patterns and ideas you see and then you start calculating. Above example from tigergutt: The g-pawn looks dangerous, but it seems not to go anywhere from the moment(Nf6 is not possible), i see the Queen is pinned and i also see the black Queen doesn't have many squares anymore(White want's to play f4)... Now you start calculcating to make these/one idea work. So you think i need to remove my Queen or make room for it, but it is not possible because Bc5 is hanging so you start thinking about Be7 to make room for your Queen.... I do some quick calculation and play Be7, it is really that simple.