Question [Q] Lg Optimus L7 P705 Custom ROM Install

Hi,
I have rooted lg optimus l7 p705 and i want install custom rom in my mobile.What are the steps for install the os.and if i am flash the mobile then this error message will come
"secure booting error".Please update how to resolve the problem and install the rom.I donot have mobile dion.I am waiting for your reply