Wobbly, pudgy, round – Everyman's diet's beginning – let's go (5-2)
I believe the answer is:
giddy-up
'let's go' is the definition.
'wobbly pudgy round everyman's diet's beginning' is the wordplay.
'wobbly' indicates anagramming the letters (I've seen this in other clues).
'round' is an insertion indicator.
'everyman' becomes 'i' (where 'Everyman' is the setter of the crossword).
'beginning' says to take the initial letters.
The first letter of 'diets' is 'd'.
'pudgy' with letters rearranged gives 'gdyup'.
'i'+'d'='id'
'gdyup' going around 'id' is 'GIDDY-UP'.
(Another definition for giddy-up that I've seen is " It's said to speed horse".)