[Q] How do you flash a ROM? Every time i do it my phone bricks topic

Im trying to flash cyanogenmod 12 on my xperia z2 but every time i flash the zip file after a full wipe the phone just doesn't turn on. I have to use flashtool to unbrick it. Its the same with another rom called moxonified, it just bricks the phone. Im really not sure what i am doing wrong. Im using TWRP. I did a factory reset and wiped the cache and dalvik cache before flashing. Im using the latest nightly build for my model number D6503. Anyone know what i am doing wrong?