4.2 is allegedly and finally dropping next week. This post has some friendly reminders concerning it.
Reduce the Sum of your Valor and Justice Points to 4,000 or Under
All Valor Points are getting converted to Justice Points and any Justice Points gained through this conversion that take the player past the 4k JP cap will simply be lost. The player will be reimbursed with 47 Silver for every lost point. As such, it can help to spend any excess points you have before the patch if you prefer heirlooms, trade goods, etc., to gold. Remember that converting VP into Conquest Points up to your weekly cap is also an option.
Incidentally, Honor and Conquest point conversions will behave a bit differently. Current Conquest Points will be converted to Honor, “possibly” past the 4k Honor cap, when the current season ends on the 28th. Only when the next season begins a week later will Honor past the cap be converted to gold. Consequently, you may be able to get away with farming Honor up to the 4k cap before the patch and thereby have a bunch of Honor ready to go to spend on season 9 gear once it too converts to Honor on the 28th. Note that any gear that requires a rating to purchase will be inaccessible come the end of season 9.
Edit 6/29/11: Yeah, so, Blizzard messed up their plan for the pvp currency conversion and it ended up behaving just like the VP->JP conversion. There is no fix; all points above the 4k Honor cap are permanently gone. Find the blue post here.
Keep Possible Spec Changes in Mind
There are no dramatic shifts for hunter dps in the patch notes, but the Careful Aim change and the fixing of the pet Focus bug may cause some players to want to change their specs. Consult your usual resources to see if anything needs changing. You can find my take here.
There is No Attunement for the Firelands Raid
You can walk right in. The attunement stuff that people are talking about are the quests in Hyjal that are necessary to open up the new sets of daily quests there. Basically, Aessina’s Miracle is the pre-4.2 quest to shoot for in order to have the dailies as ready-to-access as possible. However, it’s not necessary to have it down before the patch. For more information, check out the Wowhead guide here.
Firelands Raid Information is Already Available
LearntoRaid has guides on some of the new bosses. I’m sure they’ll have the rest of the guides up soon.
Update Your Addons
Logging onto the PTR I encountered all sorts of addon problems, far more than for a usual patch. As such, I’d suggest updating your addons before logging in on patch day or at least being ready to turn them off.