Your edges and corners, you're going to want to make sure your doing this the same. Push your mud in to each so it fulls up behind it. If you got a little crack in there you are going to want to fill that up as much as possible. It helps to join the two pieces of drywall together. Pretty much go over it like you did on the edge. Filling in the crack and pushing your mud in there. If your in experienced with this it is kind of hard to get this smooth at first but if you keep working with it, pretty soon you will get to the point where it will come out really smooth. I kind of like to do on my corners one side at a time if I am using 40 minute and if I can do it because a lot of people use corner trowels and I do sometimes but a lot times I don't simple because it takes a lot of times for me to stop and grab the corner bead and start using it and all that. It is faster for me to go by hand. If I do one side and I let it set, I can knock off the bumps on the other side and I don't get that groove that you will get if you put a coat on this side right now. If you were to put a coat on this side at the same time, then the point of your knife would press in there on the edge and it would make a groove there along the side and sometimes messes up your a little bit. So when I get a chance, I will just do one side and then I'll come back after this side hardens and then do the other side later. Either way though if you are careful and you want to both sides at the same time, you can still do it.