With a small field the format decides whether the event feels full or empty, so it is worth choosing deliberately.
This is the whole job. An announcement in the usual chess channels reaches a pool that is already mostly male, so it has to be done differently.
Start collecting entries earlier than for an ordinary event - three weeks rather than one - general organizing.
With a mixed field, one prize for first place means the same person wins every time and everyone else stops entering. Categories fix that.
Prizes themselves do not need to be large. What people keep is a photograph and a certificate with their name on it - and both cost almost nothing.
The last one is the important one. The purpose of such an event is not the evening itself but the group that forms around it - and groups form over several events, not one.
Round robin under twelve players, so nobody sits out and a small field still feels like a real tournament; Swiss above that with five to seven rounds. Rapid rather than blitz, because fields are mixed in strength and rapid keeps games competitive.
Through the women already at your club, asking each to bring one person; through chess schools, universities and non-chess communities. State explicitly that beginners are welcome, invite people in pairs, and start collecting entries three weeks ahead rather than one.
Top three overall plus categories - best unrated player above all, since that gives beginners something to play for, and best junior, veteran and newcomer. The prizes need not be large: what people keep is a photograph and a certificate with their name on it.
Often not. A women's category inside an open event is easier to fill and lets everyone play together, which many players prefer. A separate event makes sense when the aim is to build a group that will keep meeting.
Treating it as a one-off. A single evening changes nothing - the point is the group that forms around a series of events. After that, the commonest errors are announcing it too late, choosing blitz for a mixed field and offering only one prize.
Pairings are computed by bbpPairings, an open-source engine implementing the Dutch system by FIDE rules: score groups, floats on an odd field, colour alternation. Free to use.
The bot is constantly improved based on real tournaments. If you need a feature that isn't there yet, message the developers right inside the bot with the /support command. Many features appeared exactly because organizers asked for them, and useful ideas get added quickly.
Background - why women-only events exist. Formats - round robin, events for unrated players, family day.