Rinse Daily after use, brush off any external grit or grime as needed, dry and then spray or wipe down with a light coating of a dry lubricant to expel any remnant moisture and to coat the external components with a protective barrier against salt and sand adhesion. If the reel becomes submerged for a period of time or surf spray is extreme, you will want to make sure the palm side cover is rinsed and dried separately and the inside of the gear box is not contaminated.
As a preventative measure, I recommend the reel be broken down, cleaned and serviced before seasonal or extended storage or at least once a year (every 6 months if fished an average of 4 or more times a week).