The most common and most likely answer to this crossword clue is the 4 plus 5 letter word KERB DRILL
I've seen this crossword clue in The Guardian
K
E
R
B
D
R
I
L
L
Buddy explains!
The straight part
We know that "Precautions learnt by the way" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case precautions learnt by the way = kerb drill.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.