How do I solve 22 down in Daily Telegraph Cryptic 31258?

Question

Accepted Answer

22 down reads "Constituents to mingle and gather" (5 letters); the answer is GLEAN. 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.

Constituents to mingle and gather (5)

22D — Constituents to mingle and gather (5) — GLEAN