My best advice is to do significant research. WW2 is huge, and the areas of the conflict that are typically shown in general media are very limited. The actual scope, size, cultural impact and sheer amount of regions and places that were affected by the war is enormous. The perceptions people have from movies, tv shows and fiction can tend to sometimes be erroneous and stereotypical. If you go into this doing little research and mainly basing your assumptions off of a few American war movies, you're much more likely to misrepresent the conflict, and further miseducation, than you are to strike truth.

I'd emphasise to you that WW2 happened in many different countries and environments. There is no single kind of slang, no single type of battle. It wasn't just an America or British or German war. It was just as much a Chinese, Japanese, Russian, Ethiopian, Indian, Arabic, Polish, Greek, Croatian or Serbian war. Pick an area, any area really, pick a time and research everything that happened there and then in WW2. There will be no shortage of accessible books, interesting people, battles or events you can depict that an English-speaking audience might not have seen before.

China, for instance, lost 30 million people in that war. Some of the largest and most decisive battles and campaigns of the war were in China. There is no shortage of intrigue, epic struggle, humanity and compelling figures in the Chinese history of WW2. Yet I've rarely seen the Chinese theatre represented in Western Media.

Likewise, Yugoslavia, Poland, Greece, Iran, Indonesia, India etc all saw significant military actions and campaigns that are rarely if ever shown in Western media. Often times, the struggles, personal dilemmas, opinions and cultural clashes people went through were different in different areas. In many countries the war turned into a war not just against foreign nations, but a civil war as well, over their nation's future. Ordinary people, not just soldiers and politicians, were often caught in the middle, and had to go to extreme measures to survive. It is all compelling.

You have huge variety into what type of people you want to talk about as well. Resistance? Soldiers? Spies? Sailors? You could, with effort, really put a new perspective and write a new type of story for this period if you do good research.