In the previous Diablo 2 games, most players will do 'boss runs' which means killing either Baal or Mephisto (and in some cases, Diablo himself) in order to get a large amount of XP (experience points) and a lot of unique item drops so that they can complete unique sets or sell the items for money. Others prefer to kill a mob of enemies in the same area over and over again while traveling back and forth between teleporters so they can save resources such as town portal scrolls.
Blizzard has changed the way gaming in the Diablo 3 realm and offers greater and often more enticing rewards especially when grinding is concerned. Gone are the days of killing the same boss over and over again.
For starters, grinding the same spot over and over again does not yield as much returns as before. For example, there are many quests available for the game. Some of these quests tend to drop more experience points compared to just killing the same mob over and over again.
The items dropped or given as a reward is also much better and it is very important to realize that the old way of playing the game is not encouraged. Blizzard expects players to diversify their gaming style as this will add more longevity to the game.
Learn to diversify the usage of rune stones as well. You will find many different ways to customize your attack plan if you experiment with the rune stones. Some attacks will give you fire, some attacks with ice. Some will bolster its damage while others will give area of effect.
It is also good to travel in large parties to see what team combinations once can come up with which is a crucial element in team play. Mixing and matching will give much diversity.