You first see the bishop-in-front-of-rook pattern on the e-file, and then that once the bishop moves Black will find himself in check. This means the bishop in effect can have a free move, because after it moves once—and almost regardless of where it goes—Black will have to address the threat against his king by moving it or interposing something in front of it. So think about where the bishop could go on its next move that would allow it to inflict damage a move later. It’s a light-squared bishop, so look for a threat against something on a light square. The choice target turns out to be Black’s bishop on b7, because it's loose; if White can reach it in two moves he will take it for free. White thus plays Ba6+. After Black fends off the rook check, BxB wins the piece.