This topic has been mulling around in my head for a while. In light of having to address it with the submissions pool, I'm going to try and do it justice here.
A historical is so much more than placing a man and woman in an era gone by. The little things count -- more than you would probably expect.
There is a level of detail expected with a historical romance that is, by nature of the beast, overlooked in contemporary submissions. If we, as contemporary authors, put into our manuscript, "the silver pickup", we have a pretty good idea what that looks like. Yes, we can create more vivid visuals by mentioning a brand name, mentioning short or long bed, dually, or king cab. But if you're just moving a character from point a to point b, we don't necessarily need that level of detail. (Arguable, but work with me for a minute).
If you put in a historical, "They climbed into the carriage and rode away." It'll work. Maybe. But you'll have a lot more success with passing the story off as a researched historical with something like, "They climbed into the landau and rode away." Right there, the word landau, does so many things. It sets setting (1743-forward). It creates a visual (used for luxury). It gives a rough idea how many horses are in front(two), it illustrates the seating room. If you take it a step further, you can add in one word "into the five-glass landau" - and now you've added the visual of glass windows (although careful, you might have changed your setting.)
A common error I see in historical submissions is lack of enough detail to give the story a historical feel. I'm not talking about disertations on the setting/politics/class structure. I'm talking about little interwoven adjectives that make pictures pop.
Since my expertise is with ancient civilizations, let me go here to exemplify further.
Knights are a common theme as are Medieval settings. When you have characters in historicals, you must consider their perspectives (POV again).
What's a knight do for a living? War.
What are the tools he uses for war? Horses, armor, swords, spears, sometimes crossbows/arrows. Strategy.
Is a knight going to know the difference between a short sword and a bastard sword? Or the difference between a kite shield and a buckler? Or a lunge versus a thrust attack? You betcha. By sight. Without having to consider it. Second nature.
If he doesn't, chances are he's not going to survive his first battle to go on and become the fearsome knight brought to his knees by our mighty heroines.
Is a peasant going to know those things? Most likely not. A sword is a sword. They are shorter or longer. They kill -- usually friends and relatives when territories are taken over and the serfs pay for a liege lord's failure. Frankly, most peasants weren't allowed to have arms, depending on the era/feudal society and area.
And then we get into a whole different aspect of detail... era-specific tools and details. Just like one wouldn't find a zipper in the Middle Ages, we aren't going to find full plate mail immediately following the Dark Ages. The suits of armor you see in museums, aren't common until the 13th-14th century.
So if you're writing about knights "Armor" isn't going to cut it as an adjective. "Sword" isn't going to illustrate anything specific.
And if you're submitting something in this era to me, be prepared to go through that litmus test.
In conclusion -- when you are doing historical writing, research, research, research. Just like a veterinarian would know a Pomeranian by name, your historical characters are going to know the tools of their trade intimately. Use those details to illustrate the key details that draw a reader in and make them believe they are literally walking through a different era. Use it as an opportunity to show off the things you've learned when studying the era you write about. But do it effectively. Blend it in. Paint the picture. Don't make it stick out like a sore thumb.