Run your air conditioning all year round
This lubricates the seals and reduces leakage. Run your system all year, either on hot or cold depending on the temperature, it does not reduce your fuel economy

Have your air conditioning checked every year
This will highlight any problems before they become too serious

Don't ignore the problem if your air conditioning isn't working well
You may be able to tolerate weaker cooling. However, the oil within the system will not be circulating properly. Less lubrication means more internal wear and, potentially, serious damage

Fix any problems as quickly as possible
Moisture and air can get into the system, causing blockages, reduced lubrication and internal corrosion

Replace the drier / accumulator every two years or when the system has been open to atmosphere
This part readily absorbs moisture.  Once saturated, excess moisture will be free in the system, causing a range of problems.  Regularly replacing the drier / accumulator is the only way to be sure moisture levels are kept at minimum levels.