You will want to have a bottle of ammo-lock, or other ammonia neutralizer handy, along with a bucket, air line & an air valve long enough to reach from the tank to the bucket, and a net. You are also hopefully starting with a quar tank, as there may be bacteria your fish live perfectly fine with that will affect you new purchase that will be stressed from shipment. There is also the chance that there are bacteria that the new fish has that will affect your fish. Quarantine the fish for 4 weeks.
What I do when I get fish shipped in is open the bottle of ammo-lock, open the bag of fish, and immediately add the ammo-lock. The fish then go into the bucket with the water they came in. Start filling the bucket with water siphoned through the air line, using the valve to adjust for a rate of one drop per second. Once the water volume has doubled increase the rate to two or three drops per second. Decrease the drip rate if the fish is showing any signs of stress. Once you have 3 to 4 times the original volume and a fish that is behaving normally you can add the fish to the tank.
I like to start with a bare tank that has been cleaned with a bleach/water solution and rinsed well. This eliminates any bacteria that may be present from any previous fish. I also withhold food for 24 hours, and then feed lightly for the next week. Often shippers will tranquilize the fish a little, this slows down the metabolism, so they produce less waste. This also slows down their digestive system, feeding too soon and too much can easily lead to constipation.