Practice both standing at a distance ( full length mirror) and with a table top magnifying mirror until you have a good idea of which is most comfortable for you. The more you do it, the more predictable the shape will be. Sometimes you want to stand up to get the general shape and then sit down to detail. Experiment, relax and have fun. If your mind is relaxed your coordination will improve.
Ideally, the inner end is directly over the inner corner of your eye. The outer end is at a point in line with the side of your nose and the outer corner of your eye. Like this.
The right brow is easier for the right handed, so do that one first. When you do the left one, be sure to notice how you're holding your angled brow brush. Did you use the narrow side of the brush on the right brow? Check that you're using the same side of the brush for the left brow. That ensures that they will be the same thickness.
It's like riding a bike, once you get it you've got it! Practice, but don't expect perfection at first. Brows are sisters not identical twins.
