Mitres are a a very simple joint in principle but can be very tricky to cut accurately and glue satisfactorily. My most recent project, a set of interconnected birch plywood shelf boxes designed by my client, involved 28 mitred corners. To achieve the necessary accuracy I fettled every joint with a hand plane and a special sort of shooting board (see photo). The boxes were then clamped using several band clamps to achieve uniform pressure.
Although the joints were reinforced and aligned with hidden dominos (a sort of loose tenon) veneer keys were also specified as a decorative detail. A fine handsaw is used to cut at right angles across the joint and a piece of veneer (cherry in this case) is glued in and trimmed back. A handy trick to make this process a little easier is to compress the veneer with a hammer so it slides in easily – as the glue soaks in it swells back up again.