I can't download Candy Crush Saga or Farm Hero on my LG Optimus phone, but I have done it before. What should I do?
With the new updates going on and on, it is possible that the developer missed the support for this type of phone.
Try to go to Settings > Applications manager > All and locate Google Play Store and Google Play Services. Tap on each of them then tap on Clear data and Clear cache. Reboot the phone and wait for a few minutes for a full synchronization procedure while the phone is connected to the Internet then attempt another installation. It should work now.