There are regular party nights on Gili Trawangan – the various bars take it in turn to host the late night gig (up to 4AM), to ensure that everyone gets together in one place rather than being spread around. The island is small and it is easy to find everything; just ask around for where the party is going to be on any given night.
Nightlife is very laid back here, and somedays you might not notice any at all. This is very much the anti-Trawangan.
Gili Air usually has one party a week rotating at different bars during the peak season only. Locals and restaurant owners will usually mention them to you, and sometimes flyers are posted around. The party scene on Gili Air is much more low-key, and not nearly as rowdy as the wild all-nighters on Gili Trawangan