It is actually really easy to get fishing level. Just fish. It doesn't matter which region you're in, or what you're using, you will get points at the same rate everywhere. However, make sure you actually catch a fish; you only get points when you catch something. One of the easiest ways to gain level is to do fishing while waiting in battleground queues.
When fishing for fish that you cannot always catch, ensure you use a fishing lure. They're not expensive, (although will work out at a loss unless you're fishing for special fish). If you're at the bare minimum fishing level for an area, then the use of the best lure you can will make sure you rarely lose a fish. At the highest levels, you pretty much have to use a fishing lure and the best pole you can find; fishing 300 alone is insufficient to fish in Winterspring, for example!
While simply levelling up can be a long and very boring job, you can make it more interesting by searching for special fish schools. These will usually give the relevant fish type, but have a reasonably high chance of getting a box of items or stranglekelp, and all of these things can be sold at a decent profit. It also makes the fishing more intersting, since you're not stuck in the same spot endlessly.
Floating wreckage is the best source of income for fish. In particular, try to fish in the highest level areas you can; for example, it is safe to fish in steamwheedle port in Tanaris at any level (on a non-pvp server!). The items in the boxes can be very good and valuable items, such as patterns or large bags.
A rundown of where to look for schools of special fish:
There's the odd strange item you can get from fishing. Here's a list of some of them.
Perhaps not so interesting, but here's an incomplete list of locations for the standard fish types. Note that capital cities are assumed to be within their region for the purposes of this list. Region names in italics indicate a region where this fish is the most common fish in the region.
The size varies. I'm not sure about many of these, so here's merely where I've caught them.
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Last updated: 4 June 2007