1. David went home before we arrived
=> When we arrived , he had gone home.
=> After he had gone home, we arrived.

2. We had snack then we had a look around the shops
=> After having a snack , we had a look ảound the shops.

3 . The light failed the moment they began work.
=> They had no sooner begun work than the light failed.
=> No sooner had the light failed than they began work.
=> Hardly had they begun work when the light failed.