those pesky ejection marks

A good variable speed Dremel, especially the battery powered jobs, can really help with this sort of problem.

Either sanding drums or the steel tools, depending on the exact situation, are useful.

Some of the flat profile files that you get in the modelling / hobby needle file sets have a flat end rather than a point - I've found these quite handy for removing excess material from hard to access areas. If I'm wanting to remove something but leave a cleaner finish, I'll use a knife with a flexible blade to get at it, sometimes scoring/lining the excess material first so that it comes away in manageable parts, rather than trying to lop the whole lot off in one go.