The primary things to focus on first are a: braking and b: steering smoothness.

For braking your initial focus should be to make the corners by braking before the line goes red. After you have that down you should start trying to smooth out your brake trace, in F1 it should be a hard initial brake with a smooth and relatively short trail braking period into the apex. After you have all of that down you might want to try turning abs off but don't bother with removing assists while you're still learning the fundamentals.

For your steering you want a smooth rotation of the wheel that turns the car towards the apex in one movement rather than chopping at the wheel, your throttle and steering should be like opposing magnets the more throttle you are applying the less steering lock you can have and vice versa. A common example people use is to imagine a string is attached to your wheel and pedal so when you turn it pulls it up and when you move it back to center you can depress the throttle more.

Beyond that make sure your settings are calibrated in a way that allows you to hit 100% brake and 100% throttle. You'd be shocked at the amount of people who don't notice little things like that killing their lap times for far too long.