To earn gold, you can start the Arena mode or complete the different quests that are offered every day. It isn't possible to have more than 3 quests per day and you won't have any new ones while your list is full. Also, if you don't like a quest you can get a new one. So far there are 25 different daily quests to do to gain gold.

For the moment there is no way of looking at the achievements in Hearthstone! And yet the rewards are considerable. For example it's the only way of obtaining the legendary Murloc: Old Murk-Eye. Accomplishing these achievements will allow you to build up a nice hoard, with a lot of gold to boot if you manage it. So why not give it a try, because for the most part its not so difficult.
Quest Requirements Reward First Blood Complete a game in Play mode 1 Pack of cards Level Up Get any class to level 10 1 Pack of cards Crafting Time Disenchant a card 95 dust Enter The Arena Enter the Arena Free Arena entry Arrrrrr!!! Aquire every pirate card Captain's Parrot Golden Arrrrrr!!! Aquire every golden pirate card Captain's Parrot (golden) Mrglglglgl! Aquire every murloc card Old Murk-Eye Golden mrglglglgl! Aquire every golden murloc card Old Murk-Eye (golden) Chicken Dinner Win 100 games in total 300 gold Big Winner Win 1000 games in total 300 gold Ready to Go! Unlock every hero 100 gold Crushed Them All! Defeat every Expert Hero 100 gold Got the Basics! Collect every card in the basic set 100 gold One of Everything! Collect every card in the expert set 100 gold



HearthStone: Top Basic Cards - Guide to Winning in Arena
HearthStone Guide: The Paladin Aggro
Hearthstone Guide: Top 10 Combos and Card Combinations
Hearthstone Guide: Top 10 Nerfed Cards
Hearthstone Guide: Top 10 Cards to Craft