I've had the exact same problem, and I have three ugly words for you: Practice, practice and practice.
Start talking slower, make sure every word comes out of your mouth clearly and whole. It is harder to understand people who swallow their words. Then work on making your voice deeper, this takes a lot of time and concentration, but the more you work on it the faster you'll see results.
About accents you have two options, either go see a language therapist and waist a lot of money. Or you can accept yourself for who you are and start using any accent you have to your own advantage.
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http://www.solomonseagal.com
Anyone can walk into a bar and pick up a random girl.
The trick is to make the experience unforgettable to her.
A real PUA will make every women he encounters feel like she experience something once in a lifetime.