An excellent discussion of antibody titration by John Altman (Emory Vaccine Center) may be found here.
In addition, we suggest a plot of signal/noise:
Titer is affected by:–Staining volume (e.g., 100 ul)–Number of cells (not critical up to ~5 million cells)–Staining time and temperature (e.g., 30 min RT)–Type of sample (whole blood, PBMC, etc.)(Holden Maecker, Flow Cytometry Consulting)