Hi I can only tell you what I've been advised but I'm pretty new to this so hopefully someone with more experience comes along and helps too.
Float the bag with fish in, in your water for 20mins, then add a bit of your tank water to the bag with fish in, leave another 20 mins, add some more of your tank water to bag, leave a further 20 mins the using a net get fish out of bag and put in the tank. I've been advices not to tip water into your tank. Hope this is correct.