TLDR: As Ilmari said, watch replays of the fastest drivers in your races.
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Since you are a beginner, I would only focus on one of the daily series and leave the other series alone. The MX-5 Cup is a great one for example, especially as it uses a fixed setup and there are many races through out the week. While the lack of variation of using the same car for 6 weeks straight might be frustrating, by focusing on one series you will be able to improve your overall driving skill at a much quicker rate. Once you've picked a series you should first focus on being able to lap consistently at a decent pace, within roughly a 1 second window for multiple laps in a row with no crashes or major mistakes. Even if you are 3 seconds or more off pace from the fastest guys, if you can lap consistently like this then that is a great start. Being able to lap consistently is more important than being able to go 2 seconds a lap quicker but you crash every 5-10 laps or having times that vary widely from lap to lap. The ability to drive consistently helps immensely with then being able to learn how to improve lap times as you try to make adjustments to your driving, since you'll know immediately which of the changes that helped improve the lap times most.
Now onto what I found was the best ways to improve lap times when I first started racing on SRS, and that was watching replays of the race. After a race I would look up the standings, identify on what laps where the fastest times by the top drivers. I would then open the replay, switch to their point of view and watch what they did on those fast laps. While watching them I would compare what they are doing different to me, with a heavy focus on their driving line and braking points for each corner. Even though I had initially thought my driving line was okay, I always found some fundamental differences. They always used more of the track width, especially at the later stages of the straight just before they turn in and also when hitting the apex of a corner. Switching to the exterior camera in the replay also helped show this, I love the F5 camera mode in Assetto Corsa where you can then use your mouse to adjust the camera. To identify the braking point, I had the pedal app open (in the cockpit view) and paused the replay the moment the app showed braking input before the corner. I would then look around the screen and try and figure what their brake point was. For example it could be when the car passed over a line on the road or a roadmarker/tree/steward reached the edge of my monitor. Once I've identified the brake point, I would do the same thing to find the turn in point, the apex point and also the exit point. I would also note when they got back on the throttle. I repeated all this for every corner of the track. Once I finished watching the replay, I went into a practice session and tried to repeat what I had learned. Initially I would brake before the braking points on the first few laps and then try to work my way up to the point as my confidence grew.
This all might sound tedious but it honestly was the quickest way I improved my lap times and I really can't stress how important it is to watch replays. For example, I remember before one of my first races I practiced to the point where I couldn't improve my lap times anymore, even if I continued for another few hours. However in the race I was roughly 3.5 seconds per lap off pace from the leader. I spent 20-30 minutes watching the replay of the top 3 drivers. I then did a practice stint and within 10 minutes I improved my lap time by 2 seconds, which was a huge leap forward in such a short space of time. What's more, I could easily repeat it lap after lap as I already had developed my consistency for driving around the track.
Make sure in your settings for Assetto Corsa that you set the replay capture length to cover the full race. I think the default replay length is only 30 seconds to a few minutes at most. One thing to note when watching other drivers in the replays for Assetto Corsa, is that when a driver brakes the pedal app shows the brake pedal input at 100%, even if they aren't full pressed on the brakes. This used to confuse me at first and I was baffled at how they weren't locking up, until I realised the pedal app in the replay only showed either 0% or 100% braking for the other drivers.
This was a series I watched when I first started sim racing (which was about a year before I joined SRS) which slowly but purposely goes through what I mentioned above about finding a driving line, reference points and using replays:
https://www.youtube.com/watch?v=kj9Y_qdx...nZ&index=5
It's by Aristotelis who is one of the lead developers of Assetto Corsa. Aris also has his own Youtube channel, which while is main focused on ACC, it has plenty of useful information and tutorials that would apply to any sim. Here's the link to it:
https://www.youtube.com/user/Aristotelis321
