After finishing first, a ceremony is commonplace (5)
I believe the answer is:
trite
'commonplace' is the definition.
('trite' can be a synonym of 'commonplace')
'after finishing first a ceremony' is the wordplay.
'after finishing first' becomes 't' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'a ceremony' becomes 'rite' (rite is a kind of ceremony).
't'+'rite'='TRITE'
'is' is the link.
Can you help me to learn more?
(Other definitions for trite that I've seen before include "Lyre string" , "all vigour is gone" , "Overfamiliar through overuse" , "repeated too often" , "used till novelty's worn off" .)