Regardless of how many Job Agencies you unlock, it is rare to find an employee who has a score of at least 2/5. Usually, the highest score is 1.7 / 1.8. This is a rather big problem because most of the drivers with these scores earn little money. Because of that you should hire as many employees as possible and put them in cheap trucks. Thanks to that they can fulfill their working hours and increase their skills and score.
Remember that their trucks shouldn't be the cheapest and the weakest if you want to increase your drivers' scores fast. Doing that can cause your employees problems with completing a job on time which means that their score won't go up. Try to select drivers with the following skills: "Long Distance" or at least three skill points (ignore those with "Ecodriving skill").