Default z1 with 108 battery drain

i have read a lot in the forums of users claiming that their phone is lasting 1 day and used to last even 2 days, but... mine got close to 16 or 14 hours max when i first got it with android 4.2 on it, now its not getting even to the 8 hour mark, what could this be? any tips on how to make battery life better?

thanx