πολλάκις: frequent in Plato after μή and εἰ, meaning perchance.
“That we may not later, grown wise by misfortune, have to come back to sound views (ἐπιμηθεῖσθαι), but may think out the whole matter clearly beforehand (προμηθεῖσθαι).”
ᾧ: i.e. Prometheus in the myth. What is related of him Socrates will use as a model.
κατ᾽ ἀρχάς: cf. 320 b, 335 c, 348 d.