The alleys are almost randomly winding around canals and houses. So it is pretty hard to navigate your way through those alleys.
My piece of advice: check out the city map and learn ie where P Roma, Rialto, Accademia, S Marco and the Park is and how they are situated in respect to each other, so you can grasp the city in a larger scale - during day time look for the sun and how the shadows fall, this helps you to remember where roughly is north, south, east and west... and the spot you are heading togoing to a piazza off the VERY centre (S Marco), spinning around with eyes closed, then trying to get to a certain place without a map...

