Leiden International Centre: a great starting point for all kinds of aspects of living in the Netherlands. The centre can also help with matters like registration for living here or setting up a BSN appointment: https://www.leideninternationalcentre.nl/
City of Leiden Council (English language pages): a starting point for practical details like registration, getting a BSN number, documentation and topics like education, driving licences, cycling, waste management : https://gemeente.leiden.nl/english/
Huurteam for Internationals: help with all matters to do with renting somewhere to live: https://huurteamleiden.nl/for-internationals
Leiden Expats: A Facebook group where all kinds of topics, questions and events are shared: https://www.facebook.com/groups/leidenexpats
Leiden Community: Also a Facebook group – for internationals wanting to meet up with others: https://www.facebook.com/groups/612846103265401
Meeting Point Leiden – available for students who could use a little extra help finding their way in the Netherlands: https://www.universiteitleiden.nl/en/education/about-our-education/internationalisation/meeting-point
At Ease – a help centre and confidential phone line to support young people between 12 and 25 years old: https://www.ease.nl/en-index.php
City of Leiden now has an internationalisering department and plan. 13.1% of Leiden residents have a non-Dutch passport and around 33% of residents were born outside the Netherlands. You can see the plan (some is in English) at: https://leidenkennisstad.nl/portfolio-item/visie-internationalisering/