Hi,
Pretty much as already described, this is what I do:
1. Untie the bag and roll down the sides and it should then float on top of the water.
2. Leave it floating with lights off for about 10-15 mins to allow the water in the bag to slowly aclimatise the the same temp as the water in your tank.
3. As mentioned, then add a cupful of tank water into the bag every 10 mins or so, I do this for an hour to be sure, this slowly gets the fish used to your tank parameters such as PH etc, I sometimes loosely tie the bag back up each time rather than leaving it floating open, depends if your have fish that are likely to jump in the bag.
4. After an hour, or 30 mins depending on how you choose to do it, always add the fish to your tank by netting them and putting them into the tank, NEVER pour in the water from the lfs, always catch the fish one by one from the bag and move them to the tank, this just minimises any risk of spreading disease if there was any probs with the tanks at the lfs, you dont want there tank water mixing with yours.
5. Leave lights off for an hour so they feel more relaxed and less stressed, I also dont feed on the day I add fish because there is no way of knowing when the new fish were last fed at the lfs, unless you ask of course
6. Enjoy watching your new fish
Andy