Hey man, welcome to the boards.
Well, all I can tell you is what my African-American friends does.... but it's a completely different culture than actual Africa. I imagine it's pretty different culturally all throughout Africa as well, so Nigeria is also probably pretty specific.
Anyway, he always goes direct, direct, direct! In America, based on what I see with him, black girls love it. Then he persists, persists, persists! I've also noticed that image (swag) means more -- your clothes ("bling" not needed), your "image," the way you talk/walk, how much of a bad boy you are (this just means moving fast, not hiding your desire, and not being weak or crumpling to her will or other guys' will), your confidence, your ability to not be affected by something out-of-the-ordinary, ability to laugh and have fun, etc. Really, these are pretty general that could apply to any guy.
Even though I live in a different state than any of the authors (and a different country than many of the authors since only a few live in the USA), I've been able to apply GC to where I live. You just need to think about what it's like where you live and how the people interact. Since you live there, you should know the area best! What are the girls like? Shy and conservative? Loud and out-going? What are most girls into there? (dancing, watching X, etc.) How does the typical guys ask out girls there? (and how can you be different than them or do a better job of it) Where does a typical guy take a girl on a date? (and how can you refine it to be better/different)
And be weary of listening to advice from
others in the area. Just because the majority does it, does NOT mean that it's the best way. You have to find out through experience what works best in your area. You have to be a rogue and a risk-taker. The majority is not always the best.
Lastly, 20-30% isn't too bad. Approach 100 women and get 20 dates. Approach 10 girls and get 2 dates. That's not too bad. It's just a matter of learning the material and applying the material here to make those 2 dates into sex, and to try different techniques here to raise up the %. Either way, you'll always have to approach lots and never let an opportunity get away (i.e., if see a pretty girl in a coffee shop, you ask her out).
I hope this helps a bit.
What have you tried that hasn't worked? Have you tried a direct opener and than tried a indirect-direct opener and compared the results? Is your conversation good? Etc.