Get lost, missing first suitable walk (4,2)
I believe the answer is:
hoof it
'walk' is the definition.
(I know that hoof it is a kind of the walk)
'get lost missing first suitable' is the wordplay.
'get lost' becomes 'shoo' (both can be said to tell someone to go away).
'missing first' means to remove the first letter.
'suitable' becomes 'fit' (similar in meaning).
'shoo' with its initial letter removed is 'hoo'.
'hoo'+'fit'='HOOF IT'
(Other definitions for hoof it that I've seen before include "dance" , "walk" .)