How can I ensure an angle valve points in the direction I want it to?
It isn't a game of chance. A few wraps of PTFE (Teflon) tape give you the flexibility to stop at an appropriate angle. The characteristic compressibility of the tape means you don't have to bottom the joint out to make it seal. 

If you find that the joint bottoms out before it feels snug enough, start over. Remove the used tape and apply a few more wraps than last time.