Drop the -re from the infinitive and add -vo, -vi, -va, -vamo, -vate, -vano: parlare → parlavo, leggere → leggevo, dormire → dormivo. Use the imperfetto for what you used to do repeatedly, and for descriptions and ongoing background states in the past (weather, age, feelings, scene-setting), not for single completed events. The only truly irregular stem you need at this stage is essere (ero, eri, era, eravamo, eravate, erano); fare, dire and bere use their older stems (facevo, dicevo, bevevo).
Examples
- Quando ero piccolo, andavo al mare ogni estate.
- When I was little, I used to go to the seaside every summer.
- Faceva freddo e c'era molta gente in piazza.
- It was cold and there were a lot of people in the square.
- Mentre leggevo, è suonato il telefono.
- While I was reading, the phone rang.
- Prima fumavo, ma adesso non fumo più.
- I used to smoke, but now I don't smoke anymore.
The mistake to avoid
Learners use the imperfetto for a single finished action ("ieri andavo al cinema"); a one-off completed event takes the passato prossimo (ieri sono andato al cinema).
Where this fits in
The imperfect: past habits & descriptions, Italian B1: Use the imperfetto to talk about how things used to be, describe the past, and narrate ongoing actions interrupted by another event.