The best way to make sure you will get a good GW2 map is to show up in Sparkfly Fen 15-30 minutes before the event begins. To kill time, run around and farm Hard Wood and Platinum. Tags should start appearing and map chat should start organizing around 10-15 minutes before the event. If they don't, use LFG to find a Teq squad and join on their instance of the map.
Incidentally, Tequatl is the #1 best way to earn karma in Guild Wars 2. A successful Tequatl kill takes under 15 minutes, and grants four jugs/swigs/sips of liquid karma, worth 13,000 karma. Not bad, considering most events earn only 300-500 karma each. You also earn 1 gold, and have the chance at some rare and Ascended items.
Completing all of the Tequatl achievements will earn you a total of 110 Achievement Points, and "The Sunbringer" title. You will need to do at least two successful Teq runs to get all the achievements.
Most of the achievements are self-explanatory. Here are some tips for the trickier ones.
Above the Waves
This one just takes a bit of practice. Jump far in advance of the wave, as if you were planning to land on top of the wave's crest.
Have a Seat and Pull the Trigger
If you're hesitant to use a turret during the fight, don't worry. All you have to do is hop on and off to get the achievement. Do this in between phases, when you're running to and from the other events.
I Found It!
Whirlpools will only spawn during the first phase of the fight. Because they only spawn during the first phase, the longer this phase takes, the more likely it is they will spawn. Thus, this achievement is easier to get on a failing or empty map.
Whirlpools mainly spawn in the area in front and to the side of Tequatl's right foot. Listen to the NPC, who will call out "Don't get pulled under!" when whirlpools are about to spawn.
When you get sucked down, swim immediately down to the bottom and start looking around for the Sunken Chest. Move fast - the underwater poison is very damaging.
To help find the chest, hold down the Alt key, or check the box at Game Menu > Options > General Options: Show All Usable Object Names.
Interact with the chest to get the achievement. (Sorry - there's no loot.)
This is another achievement that you can only get during the first phase of the fight. The main problem is that Teq's tail swings around a lot, but only sometimes is it actually doing the flail attack. Thus, it is almost impossible to see what and when you are supposed to dodge.
The best option is to stay back by Teq's tail, dodge as often as you can, and hope for the best.