By Minibus Or Taxi
Minibuses and taxis go to Cotonou regularly and are cheap 600cfa for the 45 minute trip. You will most likely end up at the big market Dantopka in Cotonou unless you choose to descend somewhere before that. It can be quite intimidating getting out there especially in peak times. You will be immediately surrounded with people wanting to give you rides. They will grab your bags and start to usher you to their moto or car, so make sure you have a good handle on things before stepping out of the car.
Also, from the Porto Novo auto gare, there are taxis to Abomey and Lagos, Nigeria. For traveling north, head to Marche Ouanho and say you are looking for a car for your destination. Every hour or so, when filled, cars leave for Pobé and Ketou.
By plane
Although the capital of Benin, one must fly in to Cotonou and take a taxi 600cfa to Porto Novo.
By ship
There are pirogues leaving from Porto arriving less-visited lake villages nearby. Ask around down by the lagoon, about 50m east of the bridge for prices. No fixed prices, but usually expect to pay around 2,000 cfa round trip.