Openings
At around 1200 Elo, games are still decided mostly by tactics and blunders — not opening theory. So the best opening for you is one that reaches a sound, familiar middlegame with minimal memorisation, freeing your attention for the parts that actually win games.
The Italian Game (1.e4 e5 2.Nf3 Nc6 3.Bc4) gives you open, tactical positions where your improving tactics pay off. Prefer something you can play on autopilot? The London System reaches the same setup every game.
Against 1.e4, answer 1...e5 and develop naturally, or play the Caro-Kann (1...c6) for a solid structure. Against 1.d4, 1...d5 with ...Nf6, ...e6, ...Be7 and castling is clean and sound.
Pick one opening per colour, understand the first few moves, and put your study time into tactics and not hanging pieces. Play a free rated game and review it afterwards — that loop is what moves you past 1200.
The Italian Game or London System as White, and 1...e5 or the Caro-Kann as Black. At 1200, a sound, low-theory opening that you understand beats memorising sharp lines.
Tactics, by a wide margin. Most games at 1200 are decided by hanging pieces and missed tactics, not the opening. Learn a few opening moves, then focus on tactics and not blundering.