Learning how to mimic the localized speech from a geographic setting in dialogue can be very tricky.
Employing dialect, slang, and specific speech patterns can be daunting, but it is not impossible.
In my opinion, the greatest tool you have in your kit is hearing.
Need a quick and easy way to practice? If you have very young children, or have access to them, listen to how they string words together. Getting in touch with the natural syntax a child concocts while trying to talk like mommy and daddy will give you profound insights into how language is formed.
Think of listening to the way people speak as you would listen to a new song by your favorite band. The closer you pay attention, the more you will retain.