I don't know if you need to have the traits or not, but as far as I've experienced it, anyone could start to develop any Kinetic abilities as long as they concentrate and follow the practice exactly as written, although you might find it hard to accomplish if you don't have the "gift" or initial development of an ability without practice. As far as I'm concerned, umbrakinesis isn't an easy ability to master, since you need to practice a lot on your shadow manipulation, but for beginners you should concentrate on casting a shadow around you,make sure the place is big enough to see your shadow clearly, and stay away from the light so it's easier for you to repel the particles(photons I believe), just imagine millions of particles bonded forming the light in the area you want to cast the shadow on, then start repelling those particles and concentrate on one spot, although the shadow might not be as pretty as you would've liked, if you see at least a dark spot that's a start.