Malphite is an easy yet potent counter to AD melee champions, heavily relying on his ultimate. Use your ultimate for crucial engagements or favorable disengages, not just as a low-health escape.
Tank builds are generally optimal, but a full AP build can be strong against squishy teams or if your team lacks damage. Be wary of AP champions (like Rumble) and ultimate-stealers like Sylas.
Utilize your Q for effective lane poke. Comet is good for early poke, while Grasp offers sustain in melee matchups. Adapt your runes based on the opposing matchup.