Acclimating for salinity and any other water chemistry parameters. This is important if there is more than about a 0.001 difference between the water the specimen is in and your tank. Fish are generally fairly tolerant of water differences, but some invertebrates such as echinoderms can be extremely sensitive and acclimation can easily make the difference between success and almost instant death of the specimen. You usually wont know what the water difference is, so it is generally best to assume that there is a significant difference and make allowances for it. To acclimate for salinity (as well as all other water parameters such as pH), you will need to slowly add tank water to the water in the shipping bag. How quickly this is done depends on the specimen type.
For fish, many people just equalize the temperature and call it good, but if you want to be extra cautious, take the approach of allowing the temperature to equalize for about 15minutes, then open the shipping bag and add enough tank water to about double the volume of water in the bag. After about 15 minutes more, you can put the fish into the tank. You should not add the water from the shipping bag, as it may contain copper or other undesirable contaminates. I personally just restrict the end of the bag enough to let the later flow out into a pitcher while keeping the fish in the bag. Once all the water is out, the fish can be slipped out of the bag and into the water. I believe that this is easier on the fish then putting them into a bowl and netting them back out as the net can abrade the skin of the fish. Some people like to keep a quarantine tank in which they put new fish for a couple of weeks to ensure that they are disease free and eating before they put them into the main tank since it is almost impossible to catch a fish to remove it for treatment in a tank full of live rock. These quarantine tanks are sometimes routinely treated with copper to help kill any parasites. I personally am not a fan of automatically subjecting all fish to a semi-toxic bath in copper, nor do I want to risk adding the copper to the reef tank through fish transfers, etc., so I do not bother to use a quarantine tank, but an untreated one for general observation and possible treatment is a good idea if you have the facilities to set one up.
All corals, whether they are SPS, LPS or soft types seem to do well with the same 2-step acclimation process as described for fish, except that the specimen can simply be lifted out of the water and placed in the reef tank at the end of the process. Another step that can be added for SPS corals is to use a coral dip. This is a solution that you can add to the bag that will supposedly kill unwanted bacteria. I sometimes use this solution and it is difficult to know if does much good or not. Anecdotally, twice I have received frags, which almost immediately bleached. In both cases, I procured another frag from the same source and this time treated it with the coral dip. In both cases the second frag lived. My feeling is that it doesnt seem to hurt and may in fact help.
Mobile invertebrates such as shrimp, snails, starfish, sea urchins, sea cucumbers, etc. can be the most delicate when subjected to water changes. For this reason, the acclimation process is generally extended over a longer period of time with smaller water additions. The ideal case is to setup a system where a slow drip of tank water can be added to the shipping bag for a period of 1 to 2 hours. At the end of that time, the volume of water in the bag should have about tripled. If there is not enough room, some of the water in the bag should be removed and discarded. Alternately smaller quantities of water can be added by hand every 10 minute or so to accomplish the same basic task. This same process can be used with other types of specimens as well if you want to err on the cautious side.
Shrimp can almost instantly die and brittle starts can fragment their arms upon being placed in the tank if not properly acclimated. If you have these problems soon after introduction of the specimen into your tank, you need to review how you are acclimating them. Even the lowly snail is a fairly delicate creature and seldom gets the acclimation they should. That is why people sometimes have high mortality rates of their snails soon after introduction into the tank.
The one exception to not adding the shipping bag water to the tank is when working with sponges. Sponges should never be exposed to the air as it can get trapped in the structure of the sponge and cause it to die. After acclimation, the entire contents of the shipping bag should be lowered into the tank and the sponge removed underwater.
Lighting
