To save you some time and work the final coat is the only one where you need to do your angles 1 side at a time.
Regardless of what the pros use, I recommend the corner knife. It just makes your life much easier.
1st coat: apply about 3-4" mud with 6" knife to each side of corner, fold tape and apply, coat tape again with 6" knife to embed.
2nd coat: Sand any ridges in the corner left by first pass. Apply mud with 6" knife to both sides of corner, and rip it down with the corner knife. So easy.
3rd coat: You can probably avoid sanding the 2nd coat. Avoid the actual corner now, because it's about perfect. You now have about 3-4" of mud on each side of the corner. Apply the 3rd coat to the outer edge of this strip again with a 6" knife, another 3" of mud, avoiding the actual corner, finishing with about 5" of mud on each side of the corner.
The corner knife is quite flexible and will fit corners that are not exactly 90 degrees. The finished result will not be quite as crisp as a perfect corner by a top pro (because up close, the corner knife is just slightly rounded at the corner), but it's so uniform and consistent and fast, you'll be happy.