don't try to coast.
your legs will hurt for a few weeks, and then you'll have muscles you didn't know existed.
when you hit a hill, just hit it. you've got no other choice. just muscle your way up it. stuff like that is really inspiring about fixed gear...sometimes you're just drained and you hit a hill and you hammer up it and just push past where you thought you could go and unleash potential you didn't even know you had.
you may tire out from spinning all the time. same stuff applies here. just spin.
speaking of which, make sure you're spinning correctly, or you may get some pain from it.
have fun.