1. Whenever your maelstrom weapon procs to rank 5, either cast chain lightning or lightning bolt immediately (depending on how many targets there are). This is a necessity because if you don't utilize your maelstrom weapon, then you are wasting it!
2. Always use shocks effectively! This means that you use flame shock to add a DoT (Damage over Time) effect on the enemy, followed by a consistent use of earth shock to keep the nature damage debuff on the target. This debuff increases the amount of damage nature spells and attacks do, which is what your lightning bolt/chain lightning attacks are.
3. Use totems! This is a huge mistake most shamans make. They go into a raid as enhancement, and just begin doing DPS right out of the gate. If you take a few seconds to lay down the proper totems for the group, you not only benefit your DPS numbers, but also the entire raid gets buffed as well. For example, if your group primarily consists of casters, you will want to make sure you have flametongue totem and wrath of air totems down, as well as mana spring. The flametongue will boost the amount of DPS the casters do, and it will also increase the amount of damage you do from your shocks and lightning bolts. The main totem you will always want to keep down as well is the strength of earth totem, which will increase the raids melee DPS, especially yours.
4. Watch your health! Whenever you see that you are getting slightly low on health, make sure you keep maelstrom weapon stacked to 5, this will give you an instant cast heal. If you are in a raid, and there are quite a few melee DPS that are getting low on health, use your chain heal to help alleviate the healing for the healers. They will surely thank you, and your DPS shouldn't drop too considerably. After all, it is more important to stay alive and do less DPS than have a bunch of people dead. When you're dead, you aren't doing any damage!
To sum it all up, enhancement shamans are a great asset to any raid or group, because of their versatility and the boost from the totems. You can do great DPS, help alleviate the healing, and increase the amount of DPS for the entire raid/group. Enjoy playing an enhancement shaman, since the purpose of the game is to have fun!