how cool you want? more cooler you want, 'more power energy' will use. Because the compressor needs to work and keeping produce coolest air all the time. Actally the concept is same as air-conditioning, click below link to see more detail.
-DONT always open the refrig door oftenly, take ur those thing u want in once time
-Try use those refig. come with inverter type/energy save type
-DONT put so much item inside the refri til FULL, the food will take long time to be freeze or else you set the temp to 'MAX"
-Avoid the refrig located below the sunshine/contact with outside heat easily, make some gap between behind and side of it. b'coz this will affecting the compressor system working and maybe produce not so cool air in
- If ur refig. has temperature selection such as 'normal,cool and max cool'. Try to set it to 'regular cool' instead of max. b'coz it will boost more energy to produce those coolest air in