Late spring (April to June) and autumn (September to October) are the best times, with warm days, sea still swimmable in early autumn, thinner crowds and lower prices than peak summer. July and August are hot, busy and expensive as the whole island fills up, while winter is mild but wetter and quieter, with many coastal businesses closed.
Summer sun on Crete is strong, and open sites like Knossos and the harbour offer little shade. Carry water, wear a hat and sunscreen, and visit archaeological sites early or late rather than in the midday heat.
Heraklion is a real port city with busy roads, fast scooters and informal crossings, and drivers can be assertive. Cross with care and with locals, watch for mopeds when stepping off kerbs, and take extra care on narrow lanes without pavements.
Crete is very safe, but in peak summer crowds, busy markets and packed buses, ordinary pickpocketing and bag-snatching can happen. Keep your phone and wallet secure, do not leave valuables on beaches or cafe tables, and stay aware in the thickest crowds.