I start with a Vampiric Sceptre as it will help with early level jungling. Start jungling at lv1 (I usually start with wolves) and keep at it until you hit lv4, at this point you should set up a gank in which ever lane presents itself and try and get yourself at least one kill. Then contine with the jungle until you can afford to buy berserker greaves if you can't already and upgrade your vamparic sceptre.

Keep on jungling now until you can afford starks fervor, buy it and kill dragon (yes, you can do it this early as long as you spam your Q enough) if your worried then grab blue buff first to make the spamming faster. Then jungle to get your health back to full for a bit and gank again. At this point you should be able to now gank and jungle as much as you want. Hopefully, by the 15min mark you will have managed 3-4 kills and can afford your leviathan.

Now you need to make sure you get as many kills and assists as possible while staying alive to rank up those stacks. At the full 20 you will find yourself suprisingly tanky. By about the 25 min mark try to get the stacks maxed, but it will usually take 30mins. When you can buy the Sceptre and go from there. Once you have built lich bane you will do fairly large amounts of damage and your role in team fights will shine. What is it? Assassinate carries. Get in to their carry, you should be able to kill them even if you get focussed and if you do get focussed your carry will be free to PWN through their team. Kill dragon whenever it respawns to give your team the gold advantage and keep on going until you get your hextech. Once you have it you will do fairly insane amounts of damage and with enough life steal & spell vamp that you will be insanely tough.

Very late game, you can sell your leviathan and buy wamrogs but it usually won't get that far.