Before every move, you must consider all of your opponent's possible forcing replies to your move! When I was 16, I thought I had 'discovered' this key to avoiding silly tactical mistakes in OTB games. Later, when I became a chess teacher and coach, I discovered that many instructional books wisely direct readers to critically examine all the possible checks, captures and threats for both sides.
Kids are very used to solving tactics, so they often attempt to treat instructive positions as if they were simple tactical exercises: "Takes, takes, bang". But real life doesn't work that way! Your opponent also has the right to exist, and will try to fight against your ideas. Anybody suggesting the sequence starting with 1.Qxd3?? is playing what the famous teacher Dan Heisman calls "hope chess" - making a move and hoping it works.
Even at the beginning level, many chess players pick up the excellent habit of looking for undefended pieces. It is less common for young players to notice what I call 'underdefended' enemy pieces - those which are only being protected as many times as they are being attacked. Just like undefended pieces, underdefended (or badly defended, if you prefer) pieces contain the seeds of tactics for the opponent.