I will tell you how I acclimate mine rather than "give advice" and hopefully others will do the same. It is late so I hope this will still be helpful before you get started.
Before I open the box (to keep the octo comfortably in the dark), I partially fill a large bucket (I use an empty 5 gallon salt bucket because it is deep and helpful if the octo decides to get active) with water from the intended tank and draw off about a gallon more in a separate, clean container and replace the water with new saltwater.
I put my:
test strips,
hydrometer,
turkey baster,
transfer container (critter keeper)
air pump with connected air line and air stone
all on the counter next to the the partially filled bucket in the sink. Be sure you plug in the air pump and that the line will reach the bucket before you begin. I keep a set up in a bucket just for this so I don't have to go looking for enough tubing each time
I put
a pencil,
paper,
my camera,
a cup of coffee
my new electric cigarette
First meal if you are going to feed before putting it in the tank
on the opposite counter (away from the water).
I strip test my tank for PH and do a quick salinity check and write down the numbers on the sheet of paper.
When everything is where I can easily find it without leaving the room I turn off the lights (if it is daytime, working in the dark is a recipe for disaster but ambient light is better than bright light) open the box and place the bag (still unopened) into the buck of water and THEN open the bag/bags gently with a pair of scissors.
I look at the animal and see if it is breathing heavily. If I don't see it breathing but it is against the bag, I am reasonably comfortable that it is not badly stressed and is trying to hide from me. I put the air stone in the bucket and proceed to check the water. I strip test for nitrites and PH and use a hydrometer for salinity and record the numbers. Temperature is not normally a special concern when you acclimate this way as the outer water will be from your tank and should be close to ambient and the acclimation process should take about 3 hours.
Usually (assuming no problems with shipping) an overnight shipment will be OK with nitrites if there is enough water but the PH is often a problem, especially if there has been a temperature change or if the supplier does not buffer the water (this is often the case, especially in FL where it is not needed). Often the salinity will be lower than desireable (1.026). If your tank salinty is low, you will want to slowly bring it up over the next few days but the object of acclimation is to match the octos current environment to your tank so tank adjustments should not be in the mix at this point.
I prefer a turkey baster to a drip line and have use it successfully for all my Caribbean critters. I fill a turkey baster with water from the tank and add it about every 3 to 5 minutes until I have doubled the volume of water (this is somewhat dependent on how much water is in the initial bag). Once the water is doubled, I draw off half of it and repeat the process. The air stone will mix the water nicely as well as provide a release of CO2 to help keep the octo breathing well. The process is repeated until the PH and salinity match.
If you have an animal in serious breathing distress and or high nitrites add several cups of water immediately. If the octopus has inked and is still alive, quickly test the PH. If you are close, put the animal into the tank immediately unless you can rapidly create the same PH and salinity of the shipping water with clean water (usually not viable at home as usually the PH is very low and you will not likely have access to neutral PH RO water).
I like to feed before transfering but this is not common practice. Often an octopus will go into the LR and not be seen for a couple of days. I am much more comfortable knowing that it has eaten. When the water is matched, I offer a piece of thawed shrimp on a stick or a live crab and then wait 20 - 30 minutes after the octo accepts is before proceeding with the transfer.
I also recommend taking pictures at the point where you are about to transfer. It is best to NOT use a flash but I have failed to turn mine off and the octos have not inked (the pictures are better without flash so intentionally using one serves no purpose).
Move your camera to the tank room before moving the octopus so that you can get a few pictures as it comes out of the container.
When I am ready to move the octo to the tank, I put a critter keeper into the bag and "encourage" the octopus to enter. This is surprisingly easy if you can get the octo above the container and work slowly at pushing on the sides of the bag from the outside. I strongly recommend against trying to release the octo while it is in a bag. If you don't have a critter keeper I recommend finding something that will drain and has an easy on/off top. A piece of tupperware will work but you will be adding undesired but not likely damaging shipping water to your tank. Do not fasten the lid so that it is hard to remove.
Open your tank and then lift the containerized octopus out of the water and into the tank in a gentle, controlled movement. The couple of seconds out of the water will not hurt it and I have never had one to ink doing this. Place the container at the bottom of the tank and remove the top. Some animals will leave immediately but most just freeze in place for awhile. Allow it to leave at it own pace and take a few pictures at a distance.
Once it disappears into your live rock, down load your pictures, start a TONMO journal with the experience, the acclimation parameters and the first pictures and leave it alone to adjust to its new environment.