The most useful opening principles are to contest the centre, develop your pieces to purposeful squares, and protect your king. Central influence gives your pieces more choices. Development brings more of your army into the game. King safety prevents an otherwise promising position from collapsing to a forcing attack. A good move often serves two of these aims at once.
In the Italian Game, 1.e4 opens a diagonal for the bishop and claims space. After 1...e5, 2.Nf3 develops a knight while attacking a pawn. Following 2...Nc6, 3.Bc4 puts the bishop on an active diagonal and clears the way for castling. Those moves are memorable because they have jobs. If Black chooses a different defence, ask which jobs still need doing.
Avoid spending several turns moving the same piece without a reason, or sending your queen out where ordinary developing moves can attack it. These are warnings, not absolute prohibitions. A repeated move may win material or escape a threat. A pawn move may be essential to stop a pin or prepare a central break. Always calculate checks, captures and threats before applying a general rule.
A useful opening review is to pause after six or eight moves. Count your undeveloped pieces, inspect your king, and identify the central pawn breaks available to both sides. If you cannot explain your last move in those terms, replay the position and look for a more purposeful alternative. Winning the opening is less important than reaching a playable position you understand.
Try this at the board
After 1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5, explain what castling achieves and what it does not yet solve.