On a naked bike or dirt bike, I anchor the front tiedowns to the fork-tube just above the lower triple clamp, and run laterally and forward to the anchor-points. This provides for a greater angle of the strap to the tie-down point, usually, and that's good for stability. This works with some sport-bike fairings but not most.
For the rear I try to get the pull as neutral (vertical) as possible to simply secure the rear end.