Getting Players Invested

Getting players invested in the world around them is necessary if you want to tell a story. If they are only playing to kill things and gain experience/loot there wouldn't be need of a story.

Backstory

I try to work with the backstory of the PCs. Even if they are orphans with no other connections to the world they still have

• Race
• Class
• Attributes (Strength, Constitution, Dexterity,
  Intelligence, Wisdom, Charisma)
• Skills
• A specific play style (favorite powers, offensive or defensive, etc)

Engaging these elements is good start to get players involved.
For example:

• Race
  Halflings are looked down on for their size
  Tieflings may be feared
  Racial backgrounds in Player's Handbook 2 are a good source

• Class
  Paladins, Clerics, Invokers want to destroy undead, elementals and demons
  Wizards look down on sorcerer
  Druids protect nature
  Class descriptions and power sources are a good source

• Attributes and Skills
  Low-Strength characters and climbing
  Low-Dexterity characters and stealth
  Low-Intelligence characters and mindflayers

This can result in a conflict between the character and a part of the world
or in finding NPCs that share back story with the PCs.
These NPCs can become allies.

History

The world existed a long time before the PCs arrived and it has an impact on current events.

I tend to use "Show, not tell", there is no point in giving a 2 hour presentation on the history:

• Show the effects of the event
  For example, a warlord butchered a town centuries ago:
  town is in ruins, some skeletons laying on the ground, graves desecrated, ghosts hanging around, etc.
• Make it into a quest
  someone wants to have the grandson of the warlord killed.
• Reliving a memory sequence
  PCs relive the memory of ghosts so it doesn't alter history, but relives moments out of past.
  It's like time-traveling but the PCs can't change anything, the most they can accomplish is alter the perception of the memories.
• Magic items
  these can have a colorful history, for example artifacts.

It's best to break a large history in pieces so that players get the history in pieces.
And if players need to remember information it should be repeated frequently.

The history is often presented as something unexplainable. Why did... ?
So it's like putting pieces of a puzzle together. It also starts small and simple.

NPCs

The world is only as interesting as the people the PCs meet.
NPCs can become allies or antagonists depending on their goals.
It's best to give them easy and short names.
See NPC Interactions for more details.

Magic Items

Magic items have possibilities for making the world more believable:
a +1 longsword, a family heirloom given to the PCs as completion for a quest.
a +2 poison dagger to kill an ally

Magic items should correspond with the background, meaning characters should get items they need.

Visuals

Small things like monster images, maps, important writings, wanted posters make a world come alive.