One in a well, keen to pull themselves up? (8)
I believe the answer is:
aspiring
'keen to pull themselves up?' is the definition.
(as in aspiring to a better life)
'one in a well' is the wordplay.
'one' becomes 'I' (Roman numeral).
'in' indicates putting letters inside.
'well' becomes 'spring' (a well is a spring of water).
'a'+'spring'='aspring'
'i' inserted inside 'aspring' is 'ASPIRING'.
(Other definitions for aspiring that I've seen before include "Would-be" , "Ambitious, hopeful" , "Having ambition to achieve greater things" , "Wanting to get high" , "Strongly desiring to achieve" .)