When you cast towards a pool there is no guarantee that your bobber will land in the pool. Even experienced anglers often have to cast several times before their bobber lands correctly. While the place your bobber lands is somewhat random, it is also somewhat predictable:
The image (right) shows Vetchinkin's bobber distribution test. "The bobber lands with equal probability within a trapazoid shaped region." The trapazoid is an almost-rectangular area with its left and right sides at a slight angle, so the closest part of the rectangle is narrowest.
Bobbers normally land in a range between 10 and 20 yards from the angler. The calculation of distance includes height. That is only obvious if you cast while stood on a tall rock.
So, on average, you should position yourself 15 yards from the centre of the pool, facing directly towards it. Since pools are smaller than the trapazoid area in which the bobber may land, you will still sometimes miss the pool. But overall you are most likely to be be on target.
When your bobber lands within the swirling part of the pool you will catch a pool fish. But sometimes the bobber can land just outside the pool and you will still catch a pool fish. Unfortunately there is no way to be sure what you will catch if the bobber lands just outside a pool:
The target area for pools are squares, not the circles they appear as. This is not unusual for map features: For example, borders between zones are defined by a square grid (aligned North and East), even where the border is shown on the map at another angle.
Since pools only need skill 1, fish without a pole equipped. This will keep your weapons equipped, helping you defend against hostile creatures and enemy.
If you are trying to fish pools in the same area over several hours, you will need to fish all the other pool types too. This will ensure enough pools appear. Alternatively, keep on moving between different zones, or rely on other people to fish your "unwanted" pools.
If you fish pools just before the end of the world ((server maintenance)) you can cherry-pick pools, because an entirely new set of pools will appear after the end of the world ((when servers reopen)). Traditionally this was the easiest way to find certain Wreckage pools. However it now seems that when pools first appear (after the end of the world) Wreckage pools are far less likely to appear than they would when pools respawn in response to anglers fishing.
Where the factions are at war ((PvP realms)), consider the amount of enemy activity carefully. Open water fishing can be done from a quiet part of the zone, safely away from other people. Pool fishing may expose you to attack while fishing and moving.
When fishing pools in Pandaria you can gain an extra 20% catch with an Ancient Pandaren Fishing Charm active. The Charm is a gift from the Ghostly Pandaren Fisherman that rarely spawns in the Valley of the Four Winds.
Brian Westley notes, "Assuming you use an auction house 'alt' [an employee who posts sales at the auction house], it's generally better to not take items out of a trunk, since you can carry and mail it as one item." This applies to all older crates, but some of the most recent discoveries (such as Sealed Crate (Pandaria)) are bound to the angler, so cannot be mailed.