1C or less is the best for longevity. Don't store fully charged. If there's a week or so between racing, then leave them as they are after the last race. If longer, then as Beale says use the 'storage' option on your charger before storing somewhere that does not go below 5 deg C or above 30 deg C. If no storage options on your charger, discharge to about 3.4v per cell and then store.
It doesn't seem to matter if you charge the day before, but leaving cells fully charged is not helpful to a long life. For the best life, don't fully charge or discharge. Use the 'fast charge' feature on your charger. This goes to the full voltage, but doesn't squeeze in the last few drops. Cells are most susceptible to damage when fully charged or full (below 3.0v per cell) discharged. HTH
