start with shoes and some pots. try to go home after you got 1.5k and buy protector and maybe some more potions, then you buy a blasting wand and uppgrade it to rod of ages so early as possible, and then buy Sorcrers shoes (sorry i forgot them in items) and go for a needless rod or a blasting wand depends how much gold you have and get enough to rabadons deathcap. and then get a will of the ancients and a void staff, and a zhonyas as Last item,

try to farm as much minions that is possible, as more as better and beg the jungler to give you blue buff as often as possible, but still FARM MINIONS. try to get in the combo but dont be too greedy it wont be good.
and the most important HAVE FUN