I never practice offline and have never done so. It's an online simulator so that's what I want to use. And although I am definitely not a great driver I'm reasonably quick to learn a decent control of a car on a circuit.
However, when I have a new track with a new car I always observe a couple of laps of preferably one of the leaders to see how they drive, what the circuit is like, where they brake and what speeds they take corners with.
When I think I have a clue I'll jump in a car and have a go, trying to stay away from anyone driving and keeping the CTRL+S close in my mind.
I'll still struggle sometimes and have caused an occasional crash, even last weekend on a circuit I know well, just not with that car (sorry Appie!!) because I was trying to get out of the way.
When a new race starts I'll just start driving with everybody else and will improve enough to not be terrible in 2-3 races.
I've had a lot of fun races just driving midfield with somebody driving about the same times as me, but well below WR's or the leaders pace. I have fun that way and do not have the skills or desire to win a lot or become an alien.
Yes I could train to improve off line first, but the little time I have to play LFS I want to play versus other people, because that for me is where the fun is in a game. The fact that I can say "Sorry, it is my fault" to someone is a lot more fun then grumbling about AI getting in my way. Maybe that is not quite what some of you want, but I do not care if I get hit once in a while, because another race will be 5 minutes away and nothing is lost really. That might be just a mentality difference which makes LFS so much more alive when online