Talk to Everyone
Make a point of talking to everyone about everything because even the seemingly meaningless conversations can bolster other characters' opinions of you which can then make decisions easier.
Making Decisions
Although there are no right or wrong decisions you will however set in motion significant consequences either way so make sure you take as long as you need to think about them.
Click Everything
Always click on anything that is clickable as doing so will make Lee speak his mind on the object or the surrounding which in turn will give you a better understanding of the situation and how to deal with it.
Search Everywhere
There is a solution for every scenario, so if you are missing something or cannot progress further you just need to look around again more carefully.
Interact
There will be times you will be able to interact with an object or person in multiple ways, this is achieved by scrolling your mouse wheel to shift between the options.
Headshots
Always aim for the zombies heads as headshots are the quickest way to eliminate them and it saves ammo.
Replay
Every dialogue can change the next phase of the game and the storyline so consider replaying the game and make the other choices just to see what would have happened.