Conversation starter: "How to freeze a wave" (10)
I believe the answer is:
icebreaker
'conversation starter' is the definition.
(I've seen this before)
'to freeze a wave' is the wordplay.
'to freeze' becomes 'ice' (as in water turning into ice).
'a wave' becomes 'breaker' (breaker is a kind of wave).
'ice'+'breaker'='ICEBREAKER'
'how' acts as a link.
(Other definitions for icebreaker that I've seen before include "useful at beginning of party?" , "useful at parties" , "Something relieving initial tension" , "Conversation starter" , "Something to relax social tension" .)