Nasus doesn't get a lot of love in ARAM, but I always try to trade for him since I think he's actually quite strong.
9/21/0 Tanky AD masteries & runes (armor pen reds, flat armor yellows, mr per level blues, mix of Flat HP and movement speed quints.
Standard build is Trinity Force + counter-build tanky whatever the enemy team has.
Start with a good mana item like tear, or start building sheen.
Max E for pokes and try to focus on farming Q. It's never going to be as good as farming a top lane in SR, but it doesn't have to be. I usually end up with +70-100 damage on Q.
W is incredibly strong, max it second. It'll make poking incredibly easy for the rest of your team and absolutely destroys AD carries and bruisers.
I like trying to make Udyr work, but sometimes team comps don't allow it