depending on your bacteria, the OD reading is roughly linear for a good amount of values, so for example if you take a OD600 reading of your overnight culture and it is 1.0, then if you 1) do a 1:1 dilution (1 part bacteria + 1 part fresh culture media) 2) mix well and then 3) take a OD600 reading, this reading will now be ~0.5. Just perform enough serial dilutions to obtain a theoretical value of 0.02 (double checking on the actual spectrophotometer after each dilution could be worthwhile).