Sure, I'd be glad to! Here are some travel tips for your journey to Vietnam:

Best Time to Visit:
December through February is the best time for visiting Hanoi & Ho Chi Minh City due to cooler temperatures. For beach cities like Nha Trang & Phu Quoc, the best time would be from January to August, with fewer chances of rain and warmer temperatures.

Route and Accessibility:
Major airlines offer direct flights to Hanoi & Ho Chi Minh City from many parts of the world. From these cities, you can travel to Nha Trang & Phu Quoc by domestic flights.

Altitude and Acclimatization:
Vietnam's coastal cities like Nha Trang & Phu Quoc are at sea level, while Hanoi & Ho Chi Minh City aren't at a significant altitude either, so acclimatization isn't an issue.

Accommodation and Booking:
Vietnam offers a wide range of accommodations to suit every budget. It's advisable to book accommodations in advance, especially if you're traveling during peak season.

Clothing and Essentials:
Pack light, breathable clothing for Vietnam's tropical climate. However, keep some warm clothes if you plan to visit the northern regions during winter. Also, don't forget your swimsuit and sunblock for beach destinations!

Health and Safety:
Road safety can be an issue, particularly in big cities due to heavy traffic. Always follow local traffic rules. Tap water isn't safe to drink in Vietnam, drink bottled water. Carry necessary medicines/first aid & bug repellant.

Local Etiquette and Respect:
Vietnamese people appreciate modest dressing, particularly in religious sites. Learn a few basic Vietnamese phrases and respect local customs and traditions. It's customary to remove shoes when entering someone's home, and sometimes even in local shops and businesses.