The very first step to having a quality floor installation is to have a floor which is level.
This is best achieved by screeding the floor with mixture of sand and cement to get rid of any blatant uneveness in the floor.
However, if only minor correction is needed on the surface, this could be best remedied by using a good quality self leveling screed which is spread across the surface, and automatically evens out the desired area.
Leveling and smoothing a floor prior to installation gives the floor that unseen, lasting quality which can be enjoyed for many years and is absolutely critical to preventing floor failure, especially in the long term.
If there is one bit of advice that we could give to anyone who intends to have a wood / laminate floor installed... Pay extra to have your floor leveled ... be patient while you wait for it to be cured... It is worth it...