Grab a transmission with retarder equipped for the cruise tip above.
Upgrade your engine as they become available, also your tires.
Necessary upgrades - Money early game is tight. Once you get the later engine upgrades it's incredibly satisfying passing the trucks that are struggling up hills. Trust me, it's worth saving up the little bit of extra money when you're not crawling up hills, or when you're driving stop-and-go in the cities.
Get a Volvo or one of the other trucks that starts with good baseline HP. The cheapest Iveco truck is severely lacking. Watch the upper left corner to see how much time you're saving. You can also avoid 60 km speed limit country roads in Germany and manually choose to travel on the autobahn instead. The little time it takes won't make you run late on the long jobs. Open your world map once you've picked up a job and drop pins (waypoints) in towns right near your route that you haven't explored yet to unlock the truck dealerships and recruiters there. One additional tip on efficiency: On long trips you can and probably should edit your route. And remember, € / £ / $ per km is what you're after, don't just grab the highest total payout. If there are no high paying jobs, just grab a short distance job to a nearby city and try again there. This will list ONLY jobs originating in that city. Never travel empty - When you go to job selection, click on the dot on the map for the city you're in. For the really long jobs you'll have time to sleep 2 or 3 times and have time to spare for checking out new towns along your route. Hit F6 to see exactly how much longer you have before you get sleepy Most jobs will allot you enough time to sleep once, especially after you put a few points in the long distance skill, which you'll want to do early on.