Hello! It sounds like you're preparing for an exciting trip to Vietnam. I'd be happy to provide some travel tips for your visit to Nha Trang, Ðà Lạt, and Phú Quốc.

Best Time to Visit:
The best time to visit these cities in Vietnam is during the dry season from December to April. During these months, the weather is relatively stable with low humidity and less rainfall.

Route and Accessibility:
You can reach Nha Trang easily by air from major Vietnamese cities or from international locations. For Ðà Lạt and Phú Quốc, domestic flights are readily available. For all three cities, taxis and motorcycles are common modes of transportation for getting around locally.

Accommodation and Booking:
All three cities offer a range of accommodation, from budget hostels to luxury hotels. It would be wise to book your accommodation well in advance, especially if you're traveling during peak tourist season.

Clothing and Essentials:
Pack light, breathable clothing suitable for tropical weather, along with a good pair of walking shoes. Also, carry sunscreen, insect repellent, a hat, and a water bottle. As the sun can be quite harsh, sunglasses are a must.

Health and Safety:
Make sure your vaccinations are up to date before traveling. Tap water in Vietnam is generally not safe to drink, so stick to bottled water. It's also advisable to have travel insurance for any unexpected situations.

Local Etiquette and Respect:
Vietnamese people are generally friendly and reserved. Respect local customs and religious traditions. Dress modestly, especially when visiting religious or cultural sites. It's also polite to ask for permission before taking photographs of people.