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When I play Zil I usually like to go bot with a melee carry like yi, xin, fiora etc. That way I can get a little bit of farm (for aura items) and harass the other team (who is probably a range carry and some type of support) while my carry farms. Use speed up to let your carry or jungler get in and out fast. And keep hitting the CD on your ult to save for turret diving.
But all in all, your just utility. Speeds, slows and revives. Your bomb is really only good for farming and maybe the odd CS.
Zil is just one of those champs who is really only as good as who is on his team. Unless you want to rely on strangers, best to save him for Duo.