The one new thing to me was that I was asked both times to fill in online the customs declaration form (in
Official Website Direktorat Jenderal Bea dan Cukai ) and provide the resulting barcode BEFORE checking in or boarding the incoming flight.
The procedure is quite straight forward. Go to the web site, key in personal info, flight numbers etc, answer some questions (for prohibited items etc) and submit it. Once submitted the site produces a personal QR code that you have to show during checkin (or boarding if you checkin online) and at the customs once you arrive to Indo.
It is nothing to worry about - it can be done within minutes with your mobile in the airport, but I think it is better to have it ready from home.