Hope it helps and do not forget to rate and comment.
Come back again and I might have added new tips!
Step 1: Brightness
Turn the brightness on the lowest it can go.
these are the three stages.
Step 3: UMD
Step 4: WLAN
Settings > power save settings > WLAN power save > turn on.
Step 5: Auto sleep
Settings > Power save settings > Auto sleep > 5 minutes (Recommend).
Step 6: Back light auto-off
Settings > Power save settings > Backlight auto-off > 2 minutes (recommend).
Hold the screen button to turn off the screen. (This dose not shut down the PSP)
Press any button to get the screen on.