Hi, I am redirecting another great question that I received in private Dialog to the forums. I think Mariana will probably benefit from more answers than mine, and we all will benefit from the question/answers too. Unless you have a private question, it's always a good idea to post your questions in the forum so everyone can learn! (And so you don't have to wait too long for my reply!) 
Thanks!
Here's the question:
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Hi, Mariana! Great question.
Personally, I don't think there is one correct tool for this task, and I don't think you need any fancy crafting tool either. I usually just use a paring knife to gradually angle the edge, or a microplaner (fine hand grater) to fine-tune the joint or if I don't need to shave off a lot. I know some people use electric wood mitering tools for this task, but I've never had the need to invest in one. I also prefer to use kitchen tools on food items. (Though to note, most of my constructions are fairly small. So perhaps an electric mitering tool would come in handy on really large-scale constructions. I'll be interested to hear how others answer this question.)
Anyway, here's a slide from a presentation I'm giving this weekend that shows how I gradually pare down the edge with a paring knife - I hold the knife much like I would if I were peeling an apple.
When trimming or cutting baked gingerbread, I use a knife with a long serrated blade. One used for slicing bread. I've used it both in a sawing motion and shaving as Julia illustrated above with a paring knife.
I use a zester as a rasp, like you would with wood to shave down and edges of cookies I need to, including mitering. Looking for a round tool myself so I clean up rounded edges when needed.
I use a band saw to square and evenly cut all pieces that need to be mitered and fit together. This gives me exact cuts on all edges.
