Be succinct. Less is more in historical fiction – don’t get
bogged down in long descriptions or expositional dialogue.
Dump any research information that isn't relevant to your story. One reviewer praised Sarah Waters because (in The Night Watch) he knew the knobs on the radio were made of Bakelite, but she didn't say so.
Your book may be long - it may need to be long in order to address all your themes and tell a complex, nuanced story. But it shouldn't be long because you have padded it out with stuff from some archive.
In the brilliant Slammerkin, Emma Donoghue keeps description to a minimum, but vividly conveys the eighteenth century setting nonetheless. Comprehensive detail, words piled on words, aren't needed to conjure a scene. What you want is the right image, a key detail, which will stand for the greater whole.
Er, that's it. Less is more, as I say.
