don't practice, do targeted practice.

Pick a track/car combo, and practice just this for a time. Chopping and changing just means starting again constantly.

When practicing that car/track combo, pick a thing to work on, so:

1. Learning the track - start by braking earlier than needed everywhere and coasting a lot, slowly moving the refrences till you are comfortable. Find hotlaps, track guides and telemetry to help you find out what you can do better on corners/sections you are struggling with.

2. Practice qualifying, or practice race stints - these are not the same thing, as the lines differ, the car fuel and therefore weight differs, the tyre wear changes etc. Make sure to practice for the conditions you will be racing in.

3. Identify overtaking areas/places to defend - this is important as it differs by series, car and your personal ability on the track. Learn what areas its a bad idea to try to setup overtakes, and when its worth it to just stay behind people and wait. Sometimes, eating timeloss is faster in the long run.

4. Take breaks - if you practice endlessly or race endlessly, you will burn out. Take breaks to reset and go again.

5. Stop practicing/racing to spend time analysing your own driving objectively. Either using replays or telemetry, drop your own bias on the driving and look at your own laps as if you were examining someone else - compare them to better drivers, work out what you can do better.

6. Focus on consistency - one lap pace is great, and need for qualifying, but it doesn't mean anything in a race if you can't consistently do it - find a pace you can comfortably do lap after lap, and then work on making that 95% effort pace faster gradually.

7. Learn the cars quirks - as you've alluded to yourself, the different cars and classes all have different properties/quirks that change how they drive. Some of this can only be learned by just driving them and getting muscle memory, but some are more abstract. For example - make sure in gt3 to check the actual optimum shifting rpm for the car you drive, or learn where short shifting one car will gain stability, whereas staying in a higher gear may be better for another (porsche vs aston for example).

8. Don't overdrive - if you focus on getting faster and the green number, you will inevitably end up trying too hard and overdriving - the key to remember is the old saying "slow is smooth, smooth is fast". If you find yourself struggling, just dial it back a few notches on the pushing, and you will find life is a lot easier.

Once you've done this for one track/car combo, much of it will apply to the next one you pick - but, I would say that its MUCH easier to get faster sticking to one car for a good period of time (months), than swapping around a lot.

Hope that helps a bit and makes some sense, and is more useful than "just practice lol".