Dream about how to finally desert (2,4)
I believe the answer is:
go awol
'desert' is the definition.
(I've seen this in another clue)
'dream about how to finally' is the wordplay.
'dream' becomes 'goal' (I can't justify this - if you can you should believe this answer much more).
'about' is an insertion indicator.
'finally' indicates one should take the final letters.
The last letters of 'how to' are 'wo'.
'goal' going around 'wo' is 'GO AWOL'.
Can you help me to learn more?
(Another definition for go awol that I've seen is " Run off".)