Regularly on guard – true soldiers follow training (7)
I believe the answer is:
nurture
'training' is the definition.
(I've seen this before)
'regularly on guard true soldiers follow' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'soldiers' becomes 're' (Royal Engineers).
'follow' is a charade indicator (letters next to each other).
'on'+'guard'+'true'='onguardtrue'
The alternating letters of 'onguardtrue' are 'nurtu'.
'nurtu'+'re'='NURTURE'
(Other definitions for nurture that I've seen before include "Feed - support" , "Help develop and grow" , "Supply sustenance to" , "Training" , "Bring up" .)