If you feel like you're going knock the car in front of you, leaving a larger gap between it and yourself. Another reason why you feel that way maybe related to poor depth perception, thus compromising your ability to judge distances. My dad suffers from this to a degree, and he often comes very close to the car ahead of him before standing on the brakes (god bless ABS).
Don't be scare to speed up. I believe learners can only teach you how to drive, but you have to really "feel" the car to be confident. To me, when I sit in the driver's seat, my vehicle becomes an extension of my body (yes that sounds creepy, but that's exactly how I feel), and everything I do comes naturally, often by reflex.