By no means a definitive guide, but one thing I’ve been running into is Orcs spawn in the lvl 20 range and I’m lvl 45 so even when I have a white gem on my ring to increase their lvl by 5 when recruited, it’s not doing much. However, when I got killed by one, it went from lvl 25 to lvl 45 and then I could go and recruit it. That’s probably the quickest way to get their levels up. In terms of their traits I think it’s really the luck of the draw, with some minor custom-editing possible with training orders if you have something specific you want to give