I'm a beginner. I'm concentrating on hand-tool joinery for now. I've watched a lot of YouTube videos, trying to learn joinery. For the purposes of this question I'm most interested in mortice & tenon joints and dovetail joints.
When fitting a joint it's clearly necessary to remove a little wood where the joint doesn't fit yet. But, best not to remove wood that doesn't need to be removed since (e.g.) this can make the joint fit more loosely than necessary.
So the basic idea is only to remove the wood that's preventing the joint from fitting. Often, videos show people making a trial fit and then figuring out where the wood is "bruised" in order to deduce what to remove. But I can't see this bruising on the videos, myself.
At the moment I find tenon fitting seems easier, since I can do a trial fit and then wiggle the part-way-inserted tenon in the mortise to figure out where the tenon pivots; this is the high point and I can remove material from either the mortise or the tenon to make it fit (and the shoulders of the tenon will hide some mistakes in this). Sometimes, the layout marks may provide a hint as to what to remove, but that's not the case that's interesting to me here (since I already know how to do that). Anyway, in this way I can more or less fit a mortise and tenon joint without being able to spot the bruising.
However, with a dovetail joint there are multiple places where the joint could be binding during a test fit, so spotting bruising is, I suspect, more important for dovetails.
So my question really boils down to these specifics:
- How do I distinguish the wood that must be removed to fit a joint from the wood that should not?
- How do I identify where wood is "bruised"?
Pointers to learning materials would be very welcome (i.e. you don't have to explain it all directly in your answer if there are e.g. videos showing how to work on these skills).