Disgracin' the Basin
Take 3 flags in one game. Doing this Achievement should help you with the previous one. It's a great incentive for players to pay attention to the flag instead of mindlessly fighting off it. Then again, tagging it doesn't guarantee you'll stick around for it to get captured. Easily doable with a bit of effort, specially if teams are evenly matched.
Defend 3 flags in one game. Now this one isn't quite as easy as the last Achievement. First of all, when the opposing team tags the flag, it usually means that they have the superior force and that you are quite likely dead or about to die. Maybe not even anywhere near the flag at all. You will have one minute to get that back -- technically you have fifty seconds. You will be using some of that time to travel, resurrect, fight and kill enemies who would stop the tag or worse, a combination of all three. It's certainly doable, but it takes a lot of circumstances being in your favor for you to do so. Just be mindful of the flag timer. AddOns like Deadly Boss Mods for Battlegrounds are good for this.
To the Rescue!
Defend 50 flags. This is one of the more worthy Achievements because it takes a considerable amount of effort to do. As hard as Overly Defensive is, getting back a flag fifty times takes some dedication. In fact, you should treat losing games as an opportunity to complete this Achievement. One flag defended in a losing match makes it worth it.
Overcome a 500 resource advantage and win. Another difficult Achievement, even with a pre-made. If you let the opposing team get ahead by 500 points, it usually takes a 4- or 5-cap to overtake it. Deadly Boss Mods will help you track how many flags you'll need to win the game, but if it's really early, establishing and maintaining 4-cap should do it. If it's late in the game, you have no choice but to take all five flags. That's a tall order considering you're against a team that has held three or more flags long enough to jump ahead 500 points.
Win 10 times while holding 5 bases. This is another Achievement you don't necessarily have to focus on. It will just happen. 5-caps happen quite often on both sides, even with PUGs. If you want to expedite the process instead of wishing for good groups, organize a premade. Otherwise, just grind your way to those 100 wins, and it's pretty much guaranteed that you'll get enough 5-caps along the way.
Let's Get This Done
Win in 6 minutes. The simplest answer would be to play with a premade, but this is doable even with a PUG with some luck and disproportionate numbers at the beginning of the match. The only way to win within that time considering flags need one minute to get captured and start ticking is to 5-cap. Without having to go through tactics and all, just play hard, work together as a team, and this Achievement should just happen.
We Had it All Along *cough*
Win 2000 to 1990. This is an insanely difficult Achievement to get, and somewhat impossible to engineer. Even with a premade, you won't necessarily get this result -- and be on the winning side. These numbers happen when the game seesaws between three and two bases. Otherwise, this is arguably the most difficult Achievement to obtain, and players often get it as a matter of luck. If you want to screw things up for enemies, if the game is close and you're ticking too slow to win... let them take a flag. I highly encourage screwing Achievements for the enemy faction, and considering this is one of the harder ones to get, there's no reason opponents should get it at your expense.
The Defiler / Knight of Arathor
Get Exalted with the Defilers / League of Arathor. Many old school players will already have this in the bag or have a head start, specially those who experienced the old Mark of Honor turn-ins that granted reputation. On normal days, every 200 resources grant 10 reputation and on holidays such as this weekend, the reputation ticks every 150 resources. This grants a total of 100 reputation per win on normal days and 130 during the Call to Arms holiday. You're certain to get the 100 won games on the way to this if you're just starting from scratch. I'll peg this one as hard because if you'r starting from Neutral, it can be quite the grind with no turn-ins. If you got the reputation from this a long time ago, more power to you.
Arathi Basin All-Star
Assault and defend 2 bases in one game. This takes some effort and luck, but completely doable on anyone's first game. Again, the hard part is defending a flag. If you manage to do this, you might as well go for the Overly Defensive Achievement because you're not guaranteed to have easy recaps every game. Still easier than Overly Defensive because 2 flag tags are much easier than defending one.
Arathi Basin Assassin
Kill 5 players at each node. This isn't a hard Achievement as it is annoying... this requires players to constantly move from node to node, which usually means that nodes will be left empty. If all players are pursuing this Achievement, for example, nobody would be left to defend anything as it kills the chances of killing elsewhere. It's not a difficult Achievement because it's based off Honorable Kills and not killing blows. As soon as you get five at one node, simply move to another that's being assaulted. There'll be a lot of games where you'll come up short of a few, but generally, this is doable with a bit of effort. Fortunately, it doesn't require that your team win.
Arathi Basin is one of the most fun Battlegrounds, or as Elizabeth Harper puts it, "one of the least completely annoying Battlegrounds". Have fun during the Call to Arms Holiday, and pack a seasonal target dummy on your trip. Just make sure you're there to actually win the game and not just pity some fool. Even Mr. T wouldn't approve of that.