First of all, I play on PC so all of this knowledge comes only from playing on PC, though many things may be similar.
In game, there are two main ways to trading, through zone chat and through guild stores.
For zone chat, the best trading places are the zones where most people are. These are zones like Grahtwood, Stormhaven, Mournhold (have the pledge pickups and contain the alliance captial cities) and then Craglorn and most important Reaper's March and the city of Rawl'kha. Rawl'kha is unique in the fact that everything is clustered all about and so a large number of people will be found in this city at all times. For zone, just say WTB or WTS or whatever and people might answer and want to trade etc. Of course in less populated zones such a chance is less likely and it always depends on the item. (At end game, emeralds are pretty much worthless, I decon them when I get them since I always have a stack of 200 in bank).
The guild stores are spread all about where guilds can hire the traders and then people in the guild put items up to sell. However, not every zone is equal. There are a few trading hubs where the most expensive traders are (similar to the zones listed above) with Rawl'kha again being the one where the biggest trading guilds do their business (tens millions of sales weekly with millions spent to get the trader each week).
If I was in your situation I would just go to one of the most populated zones for your faction, and try to ask around in zone chat. However for the future, joining a trading guild or a couple more is a good idea if you want do to a lot of selling and just trading in general, but keep in mind in the biggest trading guilds there are requirements etc.