On the 19th of June, 2017 the EU and the UK agreed on the priorities and the structure of the negotiations under Article 50. Negotiations will first focus on citizens' rights, the single financial settlement, and other separation issues, for which dedicated negotiating groups were created.
The future trade relationship will be discussed on a 2nd phase, after the European Council decides that sufficient progress was made on the 1st phase. Negotiations will happen every month.
Here are the indicative dates for the following rounds:
2nd round: 17th July
3rd round: 28th August
4th round: 18th September
5th round: 9th October