Nothing better than great attack damage (ad) and health to keep you alive in battles. So why not have a little bite more life and ad to easily get the first blood? That runes will help you to achieve that, still better if had a dps lane partner.

Every time that I put that masteries 21/0/9 for Malphite someone tell me: "Are you crazy man? tanks need 0/21/9 or 9/21/0. But this will not work so hard to malphite. He already has granite shield to get easier your early game.

As I said, Malphite already has armor for the beginning, so get regrowth pendant to recover health and mana potion to recover it and nuke enemys if you need that. Force of nature will help you against that **** crazy mage of the other team like morgana, veigar, ap katarina, ap morde, ap teemo... After that you'll need some armor, for that: sunfire cap!
And you'll have a little problem, mid/late game, heroes will be with a little bit more of life or damage. A solution for that will be Frozen mallet, you'll avoid that your enemys run away and you'll have more 430hp to keep you alive. Bashee's veil and Atma's Impaler are my preference to late game, feel free to change that if you want or if you need.

Malphite is a very good champion to play if you know how to tank and also wanna kill. His granite shield is useful to initiate battles and take less damage. In early game fights you'll have possibility to use his first skill twice (one for initiate and two for killing), still in the team fights, use that to kill an enemy.
The best skill/spell combo is: hide in the bushes, then ultimate (unstoppable force) and his third skill (ground slam), then brutal strikes and ignite. You will attack faster and your enemys will do it slower. In the end, just use his first skill to slow enemys that had more healthy after battle or kill one who has the lowest life.