Plan for rodent, for example, found in filthy place (8)
I believe the answer is:
strategy
'plan' is the definition.
(I know that strategy is a type of plan of action)
'rodent for example found in filthy place' is the wordplay.
'rodent' becomes 'rat' (rat is a kind of rodent).
'for example' becomes 'eg' (short for 'exempli gratia', 'for example' in Latin).
'found in' is an insertion indicator.
'filthy place' becomes 'sty' (I've seen this in other clues).
'rat'+'eg'='rateg'
'rateg' put within 'sty' is 'STRATEGY'.
'for' acts as a link.
(Other definitions for strategy that I've seen before include "Overall plan for campaign" , "manoeuvres" , "Plan for achieving a particular long-term aim" , "Approach" , "Systematic plan of action" .)