Being a pit crew member requires expertise about the car you are pitting.
For example, a Mclaren-Mercedes MP4-29. If you were pitting this car, you would need to know the rate that it's tires take wear on (compared to how fast the car is going) to know when to replace the tires.
Also, you would need to know the cars weight, top speed, fuel capacity, etc.
This job offers a ton of experience in the F1 field which is required if you want to become a driver.
It also allows you to get a feel for the car.
Image: This is a crew pitting a Ferrari F 14 T
You also need to be extremely quick at your job so the driver can get those new tires you just put on onto the track.
When you finally become a driver, you should be a very experienced one. That is the reason for the high salary and trust factor. The company you race for trusts that you will take care of the car and race well.
If you follow these steps, it will assure that you will become an amazing F1 driver, be it for Mclaren-Mercedes, Lotus, Ferarri, Marussia, or any other company.
Side note: You might ask why I keep using this car in different pictures. The reason being is that it is my favorite car. For those wondering, it is a Mclaren-Mercedes MP4-29 and it is the car I hope to end up driving someday. Thanks!