After 50% increase, party slackened (5,2)

I believe the answer is:

eased up

I'm a little stuck... Click here to teach me more about this clue!

'slackened' is the definition.
(I've seen this in another clue)

'after 50% increase' is the wordplay.
'after' is a charade indicator (letters next to each other).
'd0%' becomes 'eased' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'increase' becomes 'up' (upping is a kind of increasing).
'eased' next to 'up' is 'EASED UP'.

'party' acts as a link.

Can you help me to learn more?

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app