Relax flying a kite, say, across banks of Tyne (4,2,4)
I believe the answer is:
take it easy
'relax' is the definition.
(I know that take it easy is a more specific form of the action relax)
'flying a kite say across banks of tyne' is the wordplay.
'flying' indicates an anagram (letters fly around into new positions).
'across' indicates putting letters inside.
'banks of' says to hollow out the word (remove centre letters) (the banks are the sides of the word).
'tyne' with its centre taken out is 'te'.
'a'+'kite'+'say'='akitesay'
'akitesay' anagrammed gives 'takeiasy'.
'takeiasy' placed around 'te' is 'TAKE IT EASY'.
(Other definitions for take it easy that I've seen before include "Avoid stress - remain calm" , "Put your feet up" , "Lighten up" , "Relax" , "to rest" .)