If you increase the level of the skills your Singles perform the wished activity more faster or the relationship values rise quicker. To increase the skills you need to get skill points. You get them by gathering experience points which you receive when your Singles are happy. This means their needs have to be in green are. You see a candle resp. a golden star above the concerning Single when he/she gets experience points resp. skill points.

The ability "Slacking" is a little bit confusing. It means that your Single has shorter working time but gets just as much money as before. Consequently it has no effect on the housework.