As a black American I can honestly tell you right now, "I gotta be a thug to get a black girl" is one of the biggest myths ever!
First of all, the girls who want thugs, are culturally thugs themselves. So you won't want them.
There are PLENTY of black girls that like non-thug guys of ALL ethnicities.
From first hand experience, I can tell you that the thug types of guys are more aggressive with women and will approach immediately... and that's why some of these girls date the thug. Because he asked first.
The number one piece of advice is, when u approach a black girl, treat her like u would any other girl. Don't culturally approritate by trying to drop stereotypical preferences you like, to "impress" her. Just be you. :)