The person setting up stage show initially stresses (8)

'stresses' is the definition.
('emphasis' can be a synonym of 'stress')

'the person setting up stage show initially' is the wordplay.
'the person' becomes 'me' (I can't justify this - if you can you should believe this answer much more).
'setting up' says the letters should be written backwards.
'stage' becomes 'phase' (both can mean a part or period of something).
'initially' suggests taking the first letters.
The initial letter of 'show' is 's'.
'me' in reverse letter order is 'em'.
'em'+'phase'+'s'='EMPHASES'

Can you help me to learn more?