Welcome! New shaman posters start here. (Updated Jan 1 for 5.1)
Whether you're just looking for a quick answer, or a link to get you started, you'll find what you're looking for here. Read the appropriate thread first post for a great comprehensive guide to your class:
Enhancement will need 7.5% hit and 7.5% expertise to cap for both melee and spells. At level 90 this is 2550 rating, or 2210 with a hit or expertise racial ability.
Elemental will need 15% hit to cap and not miss with spells. This can come from a combination of hit, spirit, and expertise. At level 85, it's 5100 rating points, or 4760 with a hit or expertise racial ability.
A resto shaman will be hit capped for free with the passive Spiritual Insight ability.
Reforging and gemming
The best way to reforge and choose gems for your character will depend on your current gear. The guides make some general recommendations, but dps players will get best results from simulating their own characters. Download the simulator from simulationcraft.org. Import your character from the armory, turn on scaling, and run a simulation. (More iterations will be more accurate, but slower.) Then use the scale factors you get with a tool like WoW Reforge or Mr. Robot, or an addon like ReforgeLite or Reforgenator.
Talents and glyphs have changed
You now get all your active skills and passive abilities when you choose your specialization. Talents provide situational benefits. You can reset them all at once at your trainer for the same cost as unlearning your specialization, or one at a time at any time (even in the middle of a raid) with a Tome of Clear Mind, made by scribes or purchased at a reagent vendor. The guides provide analysis into the choices available to you, or you can plan for yourself with a talent calculator. (Battle.net / MMO-Champion / Wowhead)
Prime glyphs that increase damage or healing are gone with Mists. Major glyphs have been reworked and provide situational benefits or quality of life improvements. Most minor glyphs are fun or cosmetic choices. The guides discuss your options. Here is a full list.