Practice makes perfect. I used to think (and know!) that dialogue was one of the things I was worst at, so it came as a shock when one person complimented me. Even more so when several people echoed the compliment.
It does come with time through studying how people differ in speech, by using your character's personality to differentiate, and by just practicing. Spend time with your characters and see what you can come up with. Getting feedback always helps too.
Just in response to Faith's suggestion, NEVER use fancy dialogue tags repeatedly instead of "said". "Said" is used so often in fiction that it becomes invisible. Our eyes skim over it.
Pick up the latest fiction book you read and focus on the dialogue tags - you'll be surprised how often you miss such a repeated word. It blends in and flows well. When you start using "acquiesced" instead you will draw attention away from the dialogue, and your readers will be begging for you to put down the thesaurus.
Use "said" at least 90% of the time. Reserve the alternatives for times when you want to display intense emotion, or if you do want to vary it a little. Don't forget that you can also follow dialogue with action.
I'm sure that you know this, but it was just in case Faith confused you with her response :).
Maybe think of certain characteristics someone might have. Like an eccentric person, someone who lets emotions rule their life, someone obsessed with finding love, someone who is very competitive, philisophical person. Then try and imagine how they think.
Like going off on a tangent to what they should be thinking of about impossible occurrences - maybe something they saw on a to show that could come to life. Always straying back to their characteristic even with something completely unrelated. Use certain language & dialect from wherever the character is from, Geordie slang, cockney, etc (look it up) Hope this was the sort of thing you were looking for :).
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.