Practice is obviously the main thing.
Car preparation is important. If the car handles differently every time you go out that won't help your consistency. In particular, binding suspension and a tweaked chassis will make it very difficult.
Car setup is important. Set the car up so that the rear pretty much never steps out. This will be easier to drive consistently than an oversteering car.
Choosing the right motor is important. Just because the class has a 13.5T motor limit doesn't mean you have to run a 13.5T motor. I see loads of drivers who would actually do more laps if they put a slower motor in, as they'd be more consistent and crash less.
I can also see three very different cars in your signature. I would consider dropping two of them and concentrate on one. Switching between different types of cars will make it harder to learn their characteristics and how to drive them. Your practice time, prep time and money will all be diluted between the cars. Walk before you can run
. This is a mistake I made when I was starting out; I never stuck with one car/class long enough to become any good at it.
Hope some of that is of use
