For the Bus is quite simple. You either follow the Cruise Climb Optimum Altitude table in your QRH (FPE-CCL - Inflight Performance), which gives you the optimum altitudes according to your actual weight (also based on actual Mach Nš and ISA dev), or simply use the Prog page on FMGC and follow the Optimum Alt.
I always prefer to wait until 200/300' feet below Optimum Alt and then make a small step of climb until reaching the new Optimum Alt. Repeat until reaching the top of block altitude.