I like to put the big 8 ball so the back edge is even with the first diamond. I place the two object balls between the points of the corner pocket, blocking any chance of entry.

I put the cue ball close to the blocking balls near the short rail, not quite frozen to give myself enough room to aim and hit it. I aim for about a half ball hit on the 8 ball with just enough elevation to hit about the midpoint of the 8 ball. It doesn't take a lot of force, just enough to get it up in the air.