How do I solve 29 across in Daily Telegraph Cryptic 31243?

Question

Accepted Answer

29 across reads "Cornish river levels initially drop" (4 letters); the answer is FALL. It's a letter-selection clue: take specific letters from a longer source. 'First of' means the opening letter, 'extremely' means first + last, 'regularly' means every other letter, 'oddly' / 'evenly' means odd or even positions. The full step-by-step breakdown is on this page.

Cornish river levels initially drop (4)

29A — Cornish river levels initially drop (4) — FALL