Either exactly as per the instructions :)
Or, to save time:
Sterilise bottle
Pour freshly boiled water in
Leave to cool right down.
(I prepare two or three of these sterilised cooled boiled water bottles at a time).
When ready to make up a feed:
Sterilise a bottle
Measure out powder for the feed.
Pour 1/4 of the total water amount (freshly boiled) required for the feed into the bottle with the powder. Shake thoroughly to mix.
Make up rest of feed using 3/4 of total water amount required for the feed, from the previously made, pre-boiled, pre-cooled water bottles.
It's fiddly, but it means that I can make up bottles a lot faster than one at a time, whilst still ensuring the powder meets freshly boiled water and is consumed soon after. Using part boiling but mostly cooled water means that the feed is usually the right temperature to serve immediately - but I always test it on my hand beforehand no matter what, each and every time.
That's how I do it - but I don't advocate it to anyone -it's just what I do :)