I'm wondering if there is a proper way to align/angle these bar-ends. I've seen from plane level with the handle bar to fully tilted up. Right now, my bar ends are slightly angled up. Maybe 5-10 degrees upwards. Seems to work fine.

When I had a flat-bar setup mine were about 60 degrees from flat.
But it's going to depend entirely on what's most comfortable for you, depending on how upright you want to be, how wide your bars are, etc etc.

Experiment, that's the best part of tricking out one's bike!

Put a broom stick on the top of your rear tire, then rest the other end of it on top of the handlebars ... follow that angle. Odd yes, works well though. From that point you can start moving them to suit your climbing needs.

I always set mine to the same angle as my stem. Personal prefs rule more than set standards.

For commuting I always have them on the spare bike angled so I can stop the bike using the brake levers with my thumbs.

whatever feels good to you is the best angle. Lots of different rules available, but we all use them differently.

I have mine at an angle that feels good for climbing, I have lots of hills on my commute, you might want them just for a different hand position to keep your hands from going numb.

Set them, try them, change them, the only rule is your own.

Mine are mounted on a 1" rise bar and a 3* stem. I ride a full suss mtn bike, so they are essentially used to keep me over the front wheel and in so doing, keeping my front wheel heavier during extreme climbs. There really is no 'rule-of-thumb' for bar ends. If they feel right and keep fatigue away, they are right for you.

OK thanks for the replies. I'll try a few angles. So far this one suits.

Perpendicular to your forearms.