As I prepared the surfaces of the mirror frame and inner cabinet sides for assembly, I also bored several holes for dowel pins. This will help to keep the parts aligned during glue-up. I used the same technique at the bottom of the mirror frame and the shelf (or cabinet bottom).
Using custom doweling jigs is a fairly quick way to get accurate positioning of the parts. This is important, because when it comes time to fit the drawers into the drawer pockets, the cabinet sides must be positioned just as intended or the drawer fitting will become very difficult, if not impossible. The drill press is great for boring holes into the sides of parts, but I go to the horizontal boring machine for boring holes into the end grain.
After getting all the dowel pin holes bored and rabbets cut for the back panels, I moved on to edge jointing of the bevels. Bevels on the front edges of the cabinet sides are first cut on the band saw and then smoothed and straightened with the jointer hand plane. These three images show a progression as the marks from the band saw are gradually removed by several passes of the wooden jointer.
Below, in the left image, is the set-up I used for jointing the front edges of the cabinet sides. On the right you can see I went to the block plane to smooth the beveled curve of the cabinet tops and bottom. When it comes to that final fit and finish, you can't beat the pristine sheared surfaces that are possible only with finely honed hand tools like these.