How to set the car for optimum moment for the spark-ignition time?

As the title asks, i have good compression (new piston rings + lapped valves) but feel that fuel effeciency and the power are not okay;
Some inputs : Air filter, Oil filter and the fuel filter have been changed, tires presure are checked and good. since the distributor has been removed and reinstalled i'm sure the angle has been messed up there and now i have either advanced / earlier ignition on the spark plugs, is there any tip * to get it set to the optimum timing?