With the following my laptop battery gained ~2 hours starting with the most battery draining piece (the screen).
Open the terminal and run:
sudo apt-get install xbacklight.
After you installed it run this other command:
xbacklight -set 5
If you have bluetooth and don't use it turn it off.
If you're not using WiFi turn it off too.
sudo iwconfig wlan0 txpower off
sudo iwconfig wlan0 txpower on
to turn it back on.
To make the processor drain less battery you can use the power saving feature:
echo 1 > /sys/devices/system/cpu/sched_mc_power_savings
Now, the hard disk spinning isn't energy-free so you could tune it to spin only when necessary. Run this to install Hdparm:
sudo apt-get install hdparm
then run this command:
hdparm -i /dev/sda
if you see
AdvancedPM=yes in there go on and run this other command to enable power saving for the hard disk:
hdparm -B 1 -S 12 /dev/sda
I think this is enough. Let me know if it helped.