Just make sure that every place where your world diverges does so for a good reason AND that those differences are integrated throughout your world.

The 20s and 30s are an era I'm attracted to for writing because they were a transition time; a time when ships had radio (spark gap, later shortwave) but Kong Island could plausibly exist somewhere in the Indian Ocean. It was a time things we take for granted today (like air travel) were still taking shape, and often had (travel by seaplane anyone?).

I think science fiction and fantasy set in this era has some of the same charms as steampunk, but is not so overdone yet. After all the steampunk zeppelin fixation is anachronistic for the Victorian era; the tech properly belongs to the 20s-30s. They had brass in the 20s and 30s, but they also had Bakelite, and Bakelite has its charms. It's what they made those shiny floors Fred Astaire danced on. Of course everything that is possible today was in principle possible in the 20s, so your Doc Savage team of geniuses might have something like television -- Doc's team did. You could have space travel even.

But you do want to get the stuff that is *generally* available right to get the feel right. Engineers used slipsticks; air travel was extremely uncomfortable until plains like the Ford Trimotor (1925) were introduced. Flight attendants in the 1920s were men and were called "stewards" or "cabin boys". Stewardesses came along in the 1930s, and were registered nurses.

The 20s and 30s were not only a time of rapid technological change, but social change too. In the 1920s the men who fought WW1 were still young; they came back from being gassed and shelled and some of these members of the "lost generation" turned to esoteric spiritual pursuits, others to high living (all the more exciting in the US because of Prohibition), still others to art and literature (Tolkien, Hemingway).

The 1930s was the decade when everything got grim. The dividing line was stock market crash of '29. In the year that followed there were 23,000 suicides in the US -- a record that has never been matched. There was the rise of the Fascists in Italy, of the Nazis in Germany, of Stalin in the Soviet Union, Franco in Spain, and Ultra-militarists in Japan too numerous to name. You want dastardly? Mussolini bombed the Red Cross in Abyssinia with mustard gas.

I can't begin to tell you how grim the 30s were; there was brutality, depravity and greed on a scale almost unimaginable today. There were also bravery and idealism -- often naive it is true -- that is equally hard for us to fathom.

This is more of a thing for non-fiction, but if I read a work of fiction with elements of "real life," and, say, the writer has someone do something they never did, it'd be a sticking point with me.

A movie a few years ago, I forget the name, portrayed Tom Dewey as a morbidly corrupt prosecutor---when he was so clean and incorruptible that Dutch Schultz wanted to have him rubbed out. Closer to home...Harry Turtledove wrote a book called The Guns of the South, about time travelers altering the course of the Civil War. At one point, he put a slightly-altered quote from the painter James McNeil Whistler into the mouth of Robert E. Lee---not an historical inaccuracy, but as something I recognized, I tripped over it every time I read the book.

It was such an amazing time historically, but the thing that really drew me to that time period for THIS story is the huge divide between the people that were on the cutting edge of technological advances and the people that weren't.