Support shaft between centers, mark every 6"-8". Rotate shaft; with a dial indicator (.0005 or .001) accuracy measure run out at each 6 - 8" increment. mark on shaft the run out and also mark the high spot on the shaft. Put shaft in an arbor press, supported on each end in a Vee block. Bump the shaft at the high spots. Repeat until you are happy with the straightness. Mine is +-.010 which I considered "good enough". Time an patience - good luck
