Intellect > Haste > Crit > Versatility >= Mastery
The starts depend on what gear you have, as sometimes your stat weights might be different; I would advise using raidbots to check what is best for your gear.
Haste, in general, is the best stat for destro and every other stat is somewhat even for it. But in a perfect world, you would want something around 32% haste, 700-800crit, 400vers, and 200-300 mastery.
Haste makes your cast spells quicker and reduces the cooldown of your Conflagrate. It also increases the tick rate of your Immolate. Pets also scale better the more haste you have. This is why haste is such a valued stat.
Mastery is a passive damage effect through Chaotic Energies which increases your damage dealt by a random amount.
Critical Strike increases the chances that your spells and abilities will hit with a critical hit. Your Chaos Bolt hits harder with the more critical strike you have because it always crits. So essentially it increases its damage by 1% with every 1% of critical strike you have. Pets yet again scale with critical strike and so does your Immolate which can increase shard regeneration.
Versatility is just a damage done increase and damage taken reduction.
The best way to calculate stat priorities for your character is to "sim" your characterFind out how to sim
The best race for warlock is Orc or Troll.
Flask: Spectral Flask of Power
Potions: Potion of Spectral Intellect
Health Potions: Cosmic Potion