Speed Management and Following Distance
Speed must suit the conditions, not just the limit. The posted limit is a maximum for ideal conditions; rain, poor visibility, roadworks, pedestrians or an unfamiliar road all require less. Questions often present a limit and a hazard and ask whether driving at the limit is acceptable - the answer is usually no, because the limit is not a target.
Following distance is the core measurable skill. Use the two-second rule in good, dry conditions: pick a fixed point the vehicle ahead passes, then count "one thousand and one, one thousand and two" - if you reach the point before finishing, you are too close. Double to four seconds in rain or at night, and add more when following motorcycles, heavy vehicles or when being followed closely yourself.
Stopping distance = thinking distance + braking distance. Thinking distance grows with fatigue, alcohol, distraction and speed; braking distance grows with the square of speed, so doubling speed roughly quadruples braking distance. That is why small speed increases matter so much, and a favourite exam trap: candidates underestimate how much longer it takes to stop from higher speeds.
Rule of thumb: if you cannot stop within the distance you can see to be clear, you are travelling too fast - especially on crests, bends and at night. Ease off before the hazard, not at it.