You have to be prepared before you go for your interview at the embassy. People make common mistakes, and these mistakes can delay your interview or even cause you to loose your application fee.

Those mistakes are:

1. Not coming to the embassy with your visa fee payment receipt. If you paid the fees at the bank, always remember to keep the receipt in a safe place and carry it alone with you on the day of your appointment. If you paid the fees online, you can download the receipt and print it out from your GT mobile banking platform.

2. Coming to the embassy without printing out your DS 160 form confirmation page. Always remember to print out your application confirmation page after submitting your form.

3. Not coming with the appointment confirmation. Once you have booked your appointment, make sure you come to the embassy with your appointment confirmation.

4. When booking your appointment make sure that the DS 160 form number tallies with the one on your appointment booking. This have caused a lot of people to loose their application fees. If you notice that the code which starts with AA is different from what you have on the appointment confirmation, you contact the embassy immediately.

Here is an Overview of the General Requirements for your business/tourist visa.
http://www.ustraveldocs.com/ng/ng-niv-typeb1b2.asp