Using era-appropriate slang...

I try to find slang dictionaries of the day, either written then or written as references for writers. There are usually reference materials for specific periods (like Regency or the Old West) that can make this easier.

Also, reading books and articles written in the time period that were current (like the Travis McGee series, actually, any "of the day" mystery series) is a help because those authors were using the slang of the day. Same with watching movies from the time period, if they exist. If you watch Saturday Night Live (70's), The Adventures of Buckaroo Banzai (80's), and Reality Bites (early 90's) you'd have a good basis to start with as well. Sometimes the movies are better for clothing of the period, but most of them will have some phrases that stand out now as clearly being of the day.

i am writing about the early sixties now. granted i was alive at that time but was not taking notes on popular usage. one of the things i do is subscribe to a magazine called reminisce--you can almost always find this one in a library. it helps with slang, prices, fashions, and fads. another thing i do is check out popular books from that era-just to browse. and i pull up song lyrics, old sitcom clips from youtube. one of the biggest klinkers in a retro piece is the mindset of the times. i never noticed how much the popular views and mores changed over the decades until i "re-entered" the past. kind of like mary tyler moore meets sex in the city--s6

Like the previous posters, I read sources contemporary to the era I'm writing about (the early 20th century). I've been finding great expressions and slang in diaries and letters to friends and siblings. As I'm writing, I keep a sheet of paper next to me and I jot down any word or expression that I'm not sure about, then consult the OED the next morning to be sure that they are all appropriate to the period. I have one character who is a young American and is prone to using slang, so one day I had a flip through my historical dictionary of American slang, just jotting down interesting phrases and words that were fresh in the early 20th century (bull piss=cheap liquor, take the ankle express=walk). I've been able to work some of these in and I think they've added a great period flavour to his character.

What Jeanne said. It's important not to overdo the period slang -- you want to sound authentic, not like a parody movie -- but contemporary sources will give you not only good phrases to use but also an idea of how often to use them.

I agree with what's being said. I usually use a dictionary of slang to get the phrase, but then do some research on how and when and how often it was used so I don't sound like some idiot with a dictionary and no other clues.

Some references:

Random House Historical Dictionary of American Slang by J.E.Lighter, J. O'Connor, and J.Ball

McGraw-Hill's Dictionary of American Slang and Colloquial Expressions by Richard A. Spears

Also try typing "historical american slang" into google. You'll get a TON of hits.

And keep it low-key...

What's even better is if you can coin your own phrases that seem to be 'of the period' and 'of the subculture', and take it easy on the actual slang. Actual slang is annoying in realistic doses.

Dictionaries of slang are not to be trusted. They go to great efforts to find the earliest usage, but that gives you no clue as to prevalence. Some slang terms go back for ages in certain restricted areas, but weren't part of everyday speech. Contemporary articles and letters are better--though printed material tends to lag actual usage.

The most brilliant use of contemporary phraseology is in the naval novels of Patrick O'Brian (the books take place in the early 1800s). His number-one source was letters.

You also might want to consider that a characters slang may not change too much over the years, depending on his personality. An old hippy may still say 'heavy'. Likewise an an old metalhead might also say 'heavy', though with different connotations.

A very cool AW'er gave me some advice that seems relevant:

Watch movies that were made in the time period your piece is set. This has been a HUGE help to me -- I wasn't taking notes during my childhood or young adulthood either!

Another thing I do: read popular magazines of the period. I've gone back to microfilm & read Vogue, Rolling Stone, People, TigerBeat, and perused friends' collections of EasyRider -- they don't always use slang, but sometimes will trigger a memory you can use.

Music from the era's good too. Lyricists can get away with a lot more "dated" usage than you'd find in a novel.

Have fun!
~C