Steer clear of area with invalid (5)
I believe the answer is:
avoid
'steer clear' is the definition.
(to steer clear of something is to avoid it)
'area with invalid' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'with' is a charade indicator (letters next to each other).
'invalid' becomes 'void' (similar in meaning).
'a'+'void'='AVOID'
'of' acts as a link.
(Other definitions for avoid that I've seen before include "Steer clear of, dodge" , "Prevent from happening; nullify (law)" , "Get out of" , "Fend off" , "Stay away from or circumvent" .)