Pick Your Ending/morality Guide
There are two endings in Metro: Last Light. You can get either the Redemption ending (good) or the C'est La Vie ending (bad) and it is determined by the number of morality points you have when you complete the game.
To increase your chances of getting the good ending, you need to do as many "good" things as possible while playing the game (duh). This is stuff like not killing soldiers that surrender, saving women and children, exploring, etc. You should see a white flash across the screen when you do something "good".
Below is a list to help you out. Of course if you do something bad, you will undo all the good stuff you've been doing, so check out the list of bad stuff below too.
Good Stuff / Increase Morality Points
Do what NPCs instruct to the letter
Play musical instruments
See all the visions in "Dead City"
Spare surrendering soldiers (don't kill them!)
Successfully complete "Bridge" without killing humans
Successfully complete "Facility" without killing humans
Successfully complete "Revolution" without killing humans
Successfully complete "Separation" without killing humans
Listen to the dialogue in populated areas/explore the areas
Listening to NPC stories (don't skip them!)
Save women and children
Find the hidden ammo caches on "Quarantine"
Return the crying kid's teddy bear in "Venice"
Bad Stuff/Lose Morality Points
Steal in populated areas
Kill surrendering soldiers
Successfully complete the game with a majority of good moral choices to view the "Redemption" ending. A flash of light will confirm when a good moral choice is made. If you do not make enough good moral choices at the end of the game you will instead view the "Cest La Vie" ending.