Vietnam extends about 1,025 miles (1,650 km) from North to South and 30 miles (50 km) wide East to West at its narrowest part. START IN HA NOI (North) (coolest).
Few maps cover the whole country on a single page. Best to print from Bing or Google.
The usual tourist spots are HA NOI, train to HUE, bus to DA NANG, train to NHA TRANG and train to HO CHI MINH CITY (SaiGon).
The benefit of rail travel is that you can get a SOFT SLEEPER (luggage boxes under lower bunks) ALWAYS reserve LOWER BUNKS. You can buy 'through' tickets with 'break' points (reserve to get back on the next day). HUE to DA NANG is a 4-hour bus trip. DA NANG is the stop to visit HOI AN.
Use VNPT SIM cards ($10 for SIM and $10 credit - you need a passport); FREE WiFi everywhere. Voltage 240V (regardless of socket / outlet shape). ATMs are like mushrooms - everywhere (they only dispense Dong). Make Dong 100,000 your largest paper money to avoid confusion.
GET $20 or Pounds or Euros worth of DONG AT AIRPORT ARRIVALS then use ATMs. Take VietNam Airlines bus from the airport to downtown Ha Noi. Ha Noi Taxis ARE CROOKS. ALWAYS ASK AT HOTEL (ETC) HOW MUCH TO GET TO YOUR DESTINATION. Taxi drivers always say NO CHANGE - this is a lie, they keep large money in different pockets. ALWAYS MAKE A NOTE OF TAXI PLATE NUMBER.
No need for hotel reservations (always check rooms FIRST). They need your passport for police registration. ALWAYS check your passport (yours?) before leaving the hotel.
Water cheapest from Supermarkets. (Co-Op Mart)
Because of travel delays always get to SaiGon the DAY BEFORE DEPARTURE.
Lonely Planet is unreliable (dated) websites better.
12 days is VERY TIGHT to see the MINIMUM of VietNam, 3 weeks better.
VietNam is an OPEN JAW country (in Ha Noi airport out SaiGon).
ONLY OFFICIAL WEBSITE: https://vietnam.travel/
(I have lived in VietNam for 28 years)