Watch WWII documentaries.
Dramas are acceptable, too, but don't trust them for facts--ones that are made in the 40s are pretty good for the cultural side. I've read some good fiction books on it, too--The Guns of Navarone
is a good book, except for strong language.
I'd suggest reading the stuff by people who were actually in the war.
The way I find is best for me to learn about a different time period is to read fiction written during it
first, then non-fiction about it, then fiction about
it. Roman times, though? I'm not sure there is any fiction written during. Non-fiction books are probably your best bet there.
I don't know if it's just Providence or what, but often I look up a time period in an on-line Encyclopedia or something and suddenly find something that works really well with my plot. Look for important people or events.