You can use google maps to see locations, and hopstop.com is good for directions by subway, bus, taxi (with appx. cost), walking.
Your hotel is on the south (eastbound) side of 34th St., so you would need to cross to the uptown (westbound) side and get the M34 crosstown bus, which will take you over to 12th Ave. (The M16 also goes across, but only as far as 9th Ave.) If you see the bus coming, fine. If not, you can easily grab a taxi.