Good to participate in means to control period in power (5)
I believe the answer is:
reign
'period in power' is the definition.
(I've seen this before)
'good to participate in means' is the wordplay.
'good' becomes 'g' (abbreviation).
'to participate in' means one lot of letters goes inside another.
'means' becomes 'rein' (I have seen 'Means of control' mean 'rein' so perhaps 'means' could also mean 'rein').
'g' inserted into 'rein' is 'REIGN'.
'to control' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for reign that I've seen before include "Dominion" , "Rule - dominate" , "Hold sway, rule" , "Sit on a throne" , "Occupy the throne" .)