New at gardening. Need some advice before I start

Just quickly, my house is finally built and the yard is hard. Really hard. I know it's quite clay-ey and so it won't drain well. I also dig a hole and tested the drainage. That proved how terribly hard and clay-ey the ground is.
My initial question is, I will be doing raised garden beds here and there, should I be tilling and aerating the ground before I add soils and compost into the frame or should I just lay the frame and pack it nice and deep of soil?

As for planting trees etc, I'm gonna need to till the area a little cos no root nor worms stand a chance even getting into the ground here. Leaving the soil as is or "natural" will be a waste of time I think.

Till or not?
Best plants for hard soils in temperate areas?

Thanks for your input everyone :)