To tell a stranger politely where to go, use the Lei imperative: -are verbs end in -i (giri, continui) and -ere/-ire verbs end in -a (prenda, segua). To say "don't", just put non in front: non giri qui.
Examples
- Giri a destra e continui dritto per cento metri.
- Turn right and carry straight on for a hundred metres.
- Prenda la seconda strada a sinistra.
- Take the second street on the left.
- Scusi, vada fino al semaforo e poi attraversi.
- Excuse me — go as far as the traffic lights and then cross.
The mistake to avoid
Using the tu form (gira, prendi) with someone you address as Lei sounds too familiar; note vada and prenda are irregular.
Where this fits in
Spostarsi, Italian A2: Muoversi in città e in viaggio: trasporti, indicazioni stradali, albergo e biglietti.