Learning always happens in steps. Basically steeper and flatter curves of improvement plus "plateaus" where it feels like no improvement is happening at all!
The most efficient way is to keep this learning curves as steep as possible and to overcome the plateaus as quickly as possible at the same time.
When you get thrown into something new like a new track and a new car you won't have a steep curve for your pace. You will however have a steep curve for that track and the new car as you will improve a lot every few laps.
You won't be able to work on your pace though as to be able to work on the pace, you need to be safe and consistent on the track and with the car.
Once you are safe and consistent you can start to push and try to find the last bits of time.
But at some point you will become stuck, hit a plateau without improving anymore.
Now the question will be: practice pace or practice consistency?
For consistency you should do a long stint with that car. Full tank until it's empty or the tyres are done. About 45-60 minutes just driving!
Now you will hit a plateau on your consistency too and it will be time to get some fresh input.
This can be a side by side comparison, telemetry comparison or a video by a fast driver.
Note: this fresh input is needed for every plateau so if you don't wanna practice consistency, get this before the long stint!
The most efficient way of getting faster is to get someone really fast to coach you live on track. Of course he needs to be a good teacher too and not someone who is fast but doesn't know why and where the differences are..
But that's unlikely to happen without money involved. So you're relying on forums for example like right now
You might already see: I'm not the fastest guy but I'm really good at teaching, explaining and figuring out efficient ways.
I started to play my first instrument with barely 6 years old. Kiddie songs with the flute. Abandoned it after a few years and started to play the guitar. Still doing it.
I hit a massive plateau almost 7 years ago, still couldn't overcome it. I'm at a point where the work required to play the songs I want to play is too much. And if I don't practice for a week I'm becoming worse again..
Anyway, so I know quite a bit about this stuff and misery!
Efficient practice starts with a plan and analysis. Not just driving laps over laps over laps.
The only reason to actually do laps is to make the progress you did in your head stick and to build the base for the analysis.
Most progress happens in your head! If you don't know what to do to improve it will take ages to see any progress. You will just repeat your errors over and over and burn the "false driving" into your head and body.
The question is: how can you make the most efficient progress in your head?
And that's where most of the average sim racers can't be bothered to go further. If you're asked if you'd rather spend your 2 hours of free time doing awesome fun laps in the sunset around your favorite track or to look at motec data graphs it's pretty clear what most would choose.
Well I sometimes do the second option and write 2 pages of notes, pin them next to my monitor and the next time I have 2 hours of free time I'm gonna try to check every single note!
An example of my personal inefficiency and plateau:
I just found out about the great app "Camber Extravaganza" for Assetto Corsa and took the Mazda MX-5 Cup around Magione to build an awesome setup to gain time.
I always had problems with this drifty car with its loose end combined with some understeer...
So I went on track, optimized the camber settings etc and yeah, I gained over a second compared to my personal best!
Then I asked a very fast friend of mine to try my setup vs the default setup and the result was pretty interesting.
While he was only 0.3s quicker than me with my setup and liked to drive it, he was 1.5s quicker with the default setup (compared to my PB with my setup, over 2 seconds quicker than me with default setup!).
Asked him to record motec telemetry for me so I could compare the lines and input and the result was very interesting again:
My setup had more maximum lateral G so it was a good setup in theory. The line was more steady and everything looked like my setup was really well done but the time delta showed differently...
In the end I found out that Magione has a lot of very tight corners and that his driving line was a lot tighter and therefore shorter. This tighter lines added up to quite some different distance between the lap with my setup and his lap on default setup.
It was because the loose rear end of the default setup allowed to rotate the car tighter and then drift the car out of the corners.
So he took a tighter line and was earlier on the throttle!
The tyres of the mx-5 cup can take this drifting without problems and the earlier throttle, although with some wheelspin was still resulting in a higher acceleration than the "clean" driving with my setup.
I made some spreadsheets and tried to do the same. First I became 2 seconds slower but after about 10-15 laps I started to figure out how to do it, gained time every lap until I was beating my previous PB. In the end I could again come close up to 0.3 seconds of my very fast friend!
Here's how the comparison looked like:
https://www.racedepartment.com/threads/lower-lap-time-advice-spa.146924/page-2#post-2686526
It's the second hairpin at Magione. Red line is me, white line is my fast buddy. Grey line is unimportant.
The white lines loses 0.2s through that corner but gains 0.35s on the next straight. So 0.15s gained by that cornering difference.
I know my post is long and massive but if you want to make progress you have to dig through such stuff. Otherwise you just lap around and hope to improve by random success.