While working on the Salesman’s Sugar Chest (the last project in 360 Woodworking Issue #6, read the introduction here), I used a sanding technique that is always a good one to know – in case you’ve yet to see it somewhere, or if you’ve forgot.
Light pencil scribbled over the pins and tails give you a great look at when you’ve leveled the joint. If you’re dovetailing correctly, you have the end grain of the tails sticking beyond the pin board just a skosh, and bringing that grain flush can be some work. As you sand, the pencil slowly disappears and that’s when you know both surfaces are flush.
Of course, if there’s a huge amount sticking out, by all means use a plane to level the joint. (Remember that wetting the end grain makes that task a bit easier, too.)