Honestly this is the hardest part. I tried to go to Nigeria at Christmas 2016 on a tourist visa. I had the airfare booked and was doing my research. I paid the $100 online for the E-Visa and went to the Nigerian embassy in Cairo, Egypt to claim my Visa. Unfortunately I did not have a letter of invitation from someone in Nigeria so I could not get my visa. Instead I went to Tanzania and had an amazing time.
However, I did make it to Abuja. 5 months later I was offered a job by a school in Abuja. They had an expat-quota and gave me all the paperwork so I could go to the embassy and get my visa. Still there was trouble. It took me five trips to the embassy before we could make the visa workable. Honestly the Visa process is very hard. Nobody knows why. If you are lucky enough to get one take advantage of it. If you are looking for somewhere to travel in Africa there are many countries where you can get visa-on-arrival: Uganda, Tanzania, Kenya, Egypt, Senegal, South Africa, Rwanda and many others.
But something made me realize. If the visa is this hard to get, it must be really worthwhile once you get there. Everything amazing you must work hard for.