Cleric Clerics only have 2 real choices of specialisation, Alteration and Evocation . Alteration is by far the most popular choice. It covers heals, cures, roots, and res spells. This means you'll have more heals, and be able to channel heals through on a more consistent basis. It will also reduce the mana cost of those expensive ressurection spells.
Evocation is a choice that many clerics attempting to solo decide to go for.
All the cleric direct damage spells are Evocation, this will allow more nukes for you mana, which is critical as your spells aren't very mana effecient in the first place. If you are a cleric, I heavily recommend Alteration as your specialisation. Druids Druids have 3 choices of specialisation, Conjuration, Alteration and Evocation . Conjuration is mainly useful for Druid's who solo as it is the basis for most of their DoT spells. If kiting, this can save you considerable mana and make you much more effective.