Start to earn sterling (3,8)
I believe the answer is:
get cracking
'start' is the definition.
(to get cracking is to start or begin)
'earn sterling' is the wordplay.
'earn' becomes 'get' (I've seen this in another clue).
'sterling' becomes 'cracking' (I can't explain this - if you can you should give a lot more credence to this answer).
'get'+'cracking'='GET CRACKING'
'to' is the link.
Can you help me to learn more?
(Other definitions for get cracking that I've seen before include "start flying" , "Bestir oneself" , "Prepare to break from shell" , "Start something at once" , "Start moving quickly" .)