Start with your sample and choose the modulation frequency. Then use the LIFA in live mode ('FLIM') to set the camera gain and exposure time. Change the phase to get a first impression of the sample modulation depth. Once the camera is setup correctly, one can switch the sample for the reference and take first a reference stack and then proceed with the sample for taking sample stacks. It is good practice to take another reference after your sample acquisition(s) to verify the lifetime stability of the setup. Typically, the measured lifetimes using the different references should be within 10-30 ps. Make sure that you have collected enough samples taken to be able to perform your statistics on the (average) lifetimes you have measured. Please see the LI-FLIM manual for more information (Help > Documentation).