Grabbing the trail at the very end of the public parking lot on the east side of the little town of Camogli, begin the very steep 900-stair ascent up to the Church of San Rocco. After a break to enjoy the gorgeous view, head back down the other side of the mountain en route to San Fruttuoso.
You have two trail choices at this point—the inland route is the easier option, but the coastal trail offers truly amazing views, plus the chance to explore the remains of WWII bunkers.
Whatever you choose, the trails are very well marked, so you should have no problems getting there. Just remember to bring water, as sometimes it is quite far from one pump to the next.
When you reach San Fruttuoso you have three options: hike back the way you came, catch the boat back to Camogli, or continue around the peninsula all the way to Portofino, and then bring the bus/train back into town from there.