For me the best way i have found to level is by doing all the quest in each area before you move on to the next area.
Quest and do your lvl instances
The fastest way to level up is to grind, which is killing mobs that are your level until you level. This is a quick way, but.... is incredibly boring. I suggest doing quests, and buying a leveling guide which will help you level as fast as possible. Zygors guide is the best on the market.
Don't worry about it. Just do dungeons and level up.
The easiest way to level up is to feed Pokemon Rare candies.
Pets will automatically level as you do. When you gain a level, your pet gains a level.
completing puzzles are the best way to level up.
There is no best way, just change monsters as you level up. edit: this guy is a dick thanks mister know it all
Train it.
By playing.. ;)
The best way to level at any stage of the game is to use WOW-pro! Jame's leveling guides can crank you right through in just a few days. He tells you exactly where to go, and exactly which quests to take (and which to skip). He then tells you how to do the quests!
Slayer is the easiest and best way. You train a multitude of combat skills as well as your Slayer level.
No, there is no way to play for free (completly). There is a trial edition that will let you play up to a certain level, but it is very very limited. If you want to play the game, you will have to subscribe.