Don't play too offensive and don't waste your mana to fast. Take a mana pot if you get problems with holding back your enemy. Ask your jungler for the second or third blue. Rush for Hydra and then take the boots, Randuin for tanky and the classic Black Cleaver. Then the Mallet for more AD and tanky. For lategame take Guardians Angel to stay longer in fight. At fullbuild take the red Elixir first then the blue for cooldown and ulti dmg.
Have fun and rampage!