It took me a long time to get to low 1:13's. Its hard when you are only a demo user, as your car usage is limited, especially if your not a fan of the xf cars(which on road I am not). The most important thing I learned was that the less you have to fight the car, the faster you are. The top drivers are capable with much more loose setups, where the rear end comes round a fair bit. When you first start out, you are not able to make this setup work. So you need to keep your sites realistic, find a nicely balanced setup which isnt overly difficult to drive, and use that to work your way to the 1:14's, from there you can keep going. I made this mistake, I could do 1:13's and I got given a setup from a guy doing 1:12's, i thought it would be what I needed. I used it, and felt the grip, but I was having to fight the car all the time. I actually got slower, from 1:13 when i first started with the setup I was given to 1:14, and it was only when my mate gave me his setup(who could only do a 1:14 with it) that I suddenly got better again.
Also, as I have a lot of time on my hands after (unfortunately) breaking my ankle in a tragic go kart accident(well, not tragic. More of a pathetic trudge into a tyre wall) and unable to use my steering wheel + pedals, I decided to use my laptop to play LFS on the rally x circuit. I found it much easier to get within 1 second of the lap record there(although I have to admit, the lap record is the OFFICIAL lap record, there are faster out there - I have seen it) fairly quickly. It will be easier the 2nd time around. You can use what you learn in 1 car to use in another.
In conclusion:
When you first start out, the fastest setup might not be the best for you.
Use different cars, all experience helps, and using the same car for a long period can stagnate your improvement.
And most importantly, be willing to help and be helped by others - make friends. Some people on the demo can appear to be arrogant, and annoying. But actually when you get to know them they are fine.