Every ore has a minimum required skill to successfully mine it, just like all the other skills in WoW. If you want to level your skill as rapidly as possible try to only mine (or smelt) ores that are orange or yellow at your level.
For example, when you get your skill to the point where you can mine & smelt tin ore, then stop working with copper unless you're looking for ore to sell.
Pricing of the ore: Drop by your favorite auction house and check out the prices for the various types of ore.
Depending on the server, and the demand of the moment, prices will run from about 1 gold for a stack of 20 copper ore to 20+ gold for stacks of the rarer ores (eg: Silver ore.)
Frequently the raw ore will sell for a lot more than the bars that are smelted from the ore, but not always, so check out the bars, too. Copper bars, bronze bars, silver bars, etc.
For the most part your WoW gold mining will be a two step process - mine some ore and sell it for the gold (on the Auction House.) If you are selling all your ore, rather than using it or giving it to your friendly neighborhood blacksmith, make sure you have an
auction house mule.It'll make your life much easier.
Are you using your
Mining skill to power your
Engineering skill? then you need to look at this
Killer Mining & Engineering Guide