First things first, make sure you have EUIV: Rights of Man and have it enabled. First time I completed this was complete waste of time.
Mali starts off with two gold provinces and there is a third in neighboring Kong. You want it. You probably also want to conquer Jenne to control the coast. Don't waste too much time or effort conquering neighbors left and right but instead court strong allies and stable power balance.
Focus on maximizing administrative income and unlocking the techs. Get Exploration Ideas as your first idea group, then maximize diplomatic power to relevant ideas. Diplomatic technology is also useful to extend colonial range, which might initially be a problem. Balance at your digression.
If I recall correctly settling the lone desert province between Cape Verde and the Canaries can also help extend colonial range, if Spain hasn't already nabbed it. Either way, it can help delay the Spanish (assuming Portugal scores Cape Verde as per usual).
Choosing Native Suppression policy will maximize speed, but require sizable armies on full maintenance. This will greatly increase the monetary strains of colonialism and might even force you to lower colony maintenance at times. As necessary, leverage diplomatic power to increase gold mine production and administrative power to increase tax. West Africa starts without Feudalism (+50% tech penalty) and at tech level 2 rather than 3. Having to spend more monarch power then necessary on economy, rather than on helpful techs and ideas at this point is counterproductive and so it might be argued that it's better to roll Native Coexistance and keep your armies home and scrimp on funding. I didn't do that.
You need 20 provinces, 5 in each colonial region of South America; Brazil, La Plata, Columbia and Peru. You don't need the most profitable and desirable provinces. Any 5 in a region will do, so plant yourself as far away from the bully boys as you can.