First up, beware of down time! Avoid hanging round and just waiting for things to happen like replenishing health or mana. It’s absolutely pointless running from grave to grave with no clear idea of what you goal is; this just adds to your downtime. Reduce your downtime by slaughtering anything in your path that is weaker than you. The amount of small gains that you will achieve by doing this will soon add up rather than wasting time waiting for the big kills. As you advance throughout the game you are going to find that the levels and quests are going to become far more difficult to complete. Something many people fall victim to is taking everything one step at a time. If you want to advance through the levels much quicker it is important you accept more than one quest at a time. You can drastically cut back on your time by spending a little amount of time accepting multiple quests.
The next little piece of advice I’d like to offer is to do a lot less killing and grinding and do a lot more accepting of quests.Granted, a number of the quests will expect you to kill and grind but it will be to your advantage to accept more quests where you’ll benefit greatly from the extra rewards of cash or experience or whatever else the item has to offer you.
Finally for now, make sure you complete quests two or even three levels below you rather that those above you. Even though you will receive less by way of experience etc. per kill, the smaller but more plentiful kills will soon accumulate and get you flying up through the levels quicker than you might by rushing to battle it out in the more difficult higher levels first.