My first West Africa trip went overland from Morocco, to Mauritania, Senegal, Guinea Bassam, Mali, Niger, Nigeria, Benin, Togo and Ghana. I travelled together with a french friend who was quite in a hurry since he wanted to get all the way to South Africa (he changed planes after his credit card was cancelled after using a ATM).
I went first to Rabat to meet my friend who still needed to get a visa for Mauritania, that was easy, we even got a lift from there to Laayoune in West Sahara. From there we took a bus to Dakhla.
Rabat has a interesting old town and also some Art Deco buildings built by the French.
There is a choice of 2 bus companies, i used CTM which was fairly comfortable, but no toilet in the bus, only once in while a stop for that.
CTM has every day 3 buses from Laayoune to Dakhla. Dirham 160, 8 hours, Supratours has 2 buses.