Typical Royal Marines in Angola regularly left (6)
I believe the answer is:
normal
'typical' is the definition.
(similar in meaning)
'royal marines in angola regularly left' is the wordplay.
'royal marines' becomes 'RM' (abbreviation).
'in' means one lot of letters goes inside another.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'left' becomes 'l' (common abbreviation).
The alternate letters of 'angola' are 'noa'.
'rm' going into 'noa' is 'norma'.
'norma'+'l'='NORMAL'
(Other definitions for normal that I've seen before include "Standard; at right angles" , "Popular" , "Run-of-the-mill" , "Ordinary, usual" , "Average or ordinary" .)