|Well rounded characters|
Once I have an idea for a story I place my characters into it. I have two stock characters; Gestapo Officer and Sexy Lady French Resistance Fighter. I use these over and over again. The added bonus is that I have a fifty book series revolving around these characters. They've fallen in love, fallen in love on the moon, fallen in love travelling forward in time, fallen in love in Pride and Prejudice times, fallen in love as vampires.
I know you're thinking this doesn't work, but the very strength of their characters/accent carries it off, as you'll see from this scene from Herr Flock and Mitsy Paris in 'Big Lake Cats':
"Are you going to put zat avay?" Herr Flock said, limping slowly into the room.
"Flefluffie flue, I will do whatever I want with it, my petit Lobe de l'oreille," Mitsy said, peeling the garlic.
"Vell I'm afraid I shall have to keep it, Achtung!" Herr Flock said, unbuttoning his long leather coat.
"Non, non, non, thank heaven for little girls," Mitsy said, picking up her gun.
"You shoot me in your dreams, you had better vake up and apologise," Her Flock screamed, eyes raging with rage.
Just make sure you don't stray into stereotypes; like Downton Abbey.