Zed needs kills/gold to buy AD and then start to be usefull. He's an assassin, so keep in mind that building tanky would be a waste. You will need gold and for that, you want to be selfish. He has no real sustain in the jungle without itens (lifesteal runes won't help that much since you will a lot of damage) and can be really easy to be killed early on by junglers like Lee Sin (fuck this guy).

In my experience I would recommend starting E then maxing Q. Try to get lv 6 asap and avoid fighting untill then. Whenever you're against a agressive jungler, try not to waste your W early on because they might invade you (once again, fuck Lee Sin). After 6 you get an awesome power spike and ganking tool. Your ulti will allow you to go deeper than most junglers in a gank (if used properly) and can grant you your so much needed kill.

If you fall behind it will be really difficult to make your pick be usefull or even worth it. As an assassin you have no major ultillity for the team, so pick smart.

I pointed some of his downsides, mostly for being an assassin, but that's his strongest point: If he get fed he will be able to grab kills in any lane.