Why are you worried that they might not grant you a visa simply because you know someone in the U.S.? Unless you are going on a business trip where you have paid for the hotel and have huge cash reserves, it's a requirement for you to know someone in the U.S. It's the person that you know that's "supposed" to send you a letter of invitation. In fact, when you go for the interview, they may ask how well you know the person that wrote the letter of invitation in order to establish the relationship. At any rate, what the consular officer is looking for is for you to convince him or her that you are not going to abscond on getting to the U.S. Just be yourself man. They're human just like you. Hope this helps?

During the interview, you should state clearly your main purpose of travelling to US and you must be able to CONVINCE the Visa Officer that you have substantial reasons and documentary evidence to prove that you have the intention of coming back to Nigeria your home country. Wish you goodluck!

When our country is rid of lies here and there going for visa interview will be like going for a chat with a friend. As you have been rightly advised just be yourself and make your intention clear. Give enough evidence that you wish to return home that is the ultimate. All the best.