So you've been kicked from a heroic and yelled at to "enchant ur gear nub." We can help. We meaning your local enchanters. Here are the steps to a smooth transaction. If you're not a people person, see Alternate Guide A.
How to Buy an Enchant
1) Figure out which enchant you want. This may be several enchants based on cost or availability of mats. For example, while there are better enchants, greater savagery is somewhat cheap and a good choice for leveling weapons. Or maybe you're a lowbie in which case I have to point you in another direction: see Alternate Guide B. If you're just looking for a glow, look up beastslaying, it's cheap and gives a nice red glow. There are several ranks with higher ones giving more visible glows. Alternatively if you want blue go for Striking, it gives +X to your weapon's damage and again, is more visible at higher ranks.
2) Look up the materials. I use www.wowhead.com.
3) Get the materials. There are several ways to do this.
3a) Buy them directly from the AH or trade channel.
3b) Hire an enchanter to DE some items for you. With luck you'll get what you need. Don't forget to tip.
4) Find an enchanter. Rather than a generic "LF enchanter" instead say "LF enchanter for [enchant]." If you're looking for many enchants, try something like "lf high level enchanter to link book." Then you can search through all the enchants they can do.
4a) Check your realm forum for a list of crafters. There will often be a list of people with the rarest enchants.
5) Figure out where to meet and agree on which enchants you're getting.
6) Hand over mats. Some enchanters prefer one set at a time, I do. It allows the enchanter to easily tell if you're given the right mats.
7) Put the item to be enchanted it "will not be traded."
8) Put some gold in the currency area. Some enchanters will give a price in advance, others expect tips, and some work for free with mats, most often if they're leveling up. How much? It depends. Start at 10g if you're above level 70 and work up from there if the enchant is rare or if the enchanter had to travel or wait a long time. If you're a lowbie, don't worry so much; don't bankrupt yourself, but if a tip would bankrupt you, maybe you need to shift priorities. If you're a twink, tip well; if the enchanter is going to sell his soul to help you in your quest to ruin the game for new players the least you can do is make him rich.
9) Thank the enchanter.
Why did I make this?
Well to start off, I'm an enchanter. I like to help people, but it's asking a lot when someone sends a vague tell like "what enchants do you have for a rogue?" The problem here is that I don't know what sort of budget you have: like I said there are basically two tiers of WotLK enchants: good but cheap and great but bye bye gold. I don't know what enchants are best for rogues and even if I did, I might not have the best, so I offer what I can. I've run into people who give nothing, not even a thank you. I've run into people who know what they want, but it's a terrible idea (most of the battlemaster enchants I've done have been for hunters) due to effectiveness or cost.
Long story short: I've had preventable bad experiences as an enchanter. Not to lay it all on the enchanter: Enchanters, you can now link your books in trade, so save everyone's time and don't say "enchanter lf work" when you could say "[skill] enchanter lf work [book]"
Alternative Guide A
Look on the AH for a scroll which has your desired enchant. It will have a name like Scroll of [enchant name].
Alternative Guide B
Rather than using my time and your gold: find someone to do it for free. Who would give out free enchants? Lowbie enchanters. Hang out in a main city and you might find someone screaming his poor lungs out looking for someone to enchant. He's trying to level and wants to avoid wasting mats. He gets a skillup, you get an enchant, everyone wins. Well, except me, I get more competition. :P
Good luck and have fun with your glowy new weapon!