For Ashes to Dust and Skin-Deep, applying scavenge charm to dust-able and skin-able creatures will increase the success rate of dusting by 25% which will speed up the time it takes to reach 500 successful attempts.
For the Master Shapeshifter, simply go into the room and click the Shape Changer until you’ve changed into all 8 creatures and walked though the respective portals. You don't have to stick with the first creature you change into. If you get a repeat creature, just use the wand again until you get a creature you haven't done yet. This way you can earn the achievement doing to event 1 time.
For Santa’s Li’l Helper, many don’t realize you can buy the 25 Christmas Bundles from the Messenger of Santa NPC.
For Shell Seeker, the items you get out of the large turquoise shell on Oskayaat also count towards the achievement which could potentially halve the time it takes earn the achievement since you can use 2 shells per day instead of one.
For Superstitious, you can use more than 1 Mysterious Voodoo Skull since the cooldown only applies to the item and not your character. Just buy a few Mysterious Voodoo Skulls to speed up the process.
There are a few achievements where you can place a weight on your keyboard and just walk away. These achievements are:
Waverider- When heading towards Misguided, there is a water vortex where you can complete this achievement by weighing down the up key and your character will continue swimming back and forth between the two sides of the vortex.
ENTRANCE SIDE
MISGUIDED SIDE
Minstrel and Rockstar- You can put a musical instrument on a hotkey and weigh down that key to play the instrument.
Quick as a turtle- You can weight down an up or right key depending on the position of the turtle and your character will just walk back and forth between the 2 islands.
Deep Sea Diver- In Yalahar Sunken Quarter, you can wedge your character in the tower here and weigh down the up and down key. This will cause your character to walk back and forth continuously. Just make sure you keep your diving or Depth Galea on so your character doesn't down.
Xarkost made a video of this on YouTube (https://youtu.be/HQUvatAMrGg?si=m9-ggyxvpNUf6UAe)
Note: This may not work on certain keyboards. I was able to do it on a standard keyboard but not a mechanical keyboard.
The same setup can be used for Firewalker at Kazordoon blessings. You just need to make sure your Firewalker Boots are charged or you could kill your character if they run out!
Xarkost has made a great video demonstrating this technique (https://youtu.be/kQALIlcz99I?si=AxS45ck7SoH-UYeV)
You could do the Deep Sea Diver and Firewalker achievement at the same time by fire bombing your path in the Sunken Quarter however this does mean you'll need to monitor the bombs to ensure they don't go out.
Happy Achievement Hunting!