1. Decide how to get there. Go to Hanoi City (which is the capital of Vietnam) and choose the transportation type.
The best option is bus. It is cheap, comfortable and comes with safe driver. A tourist bus is strongly recommended; the price is around 8 USD each way and 15 USD for a round trip. The local buses are cheaper, about 4-6 USD per way but they are worse. Rental car and Seaplane are also other available choices.
2. Decide on the duration of the stay
A tour in Halong Bay can be for 1 day, 2 days 1 night, or 3 days 2 nights. However, 2 days 1 night or 3 days 2 nights trip is preferable; you can have more time to stay in Halong City or Cat Ba Island.
3. Choose your accommodation
You can choose to stay on a cruise that offers overnight cabin with absolutely good condition like a three to five stars hotel. Another option for accommodation is the hotel or bungalow on Cat Ba Island.
4. Know about the food
Most of the food is seafood, of course. Otherwise, meat and vegetables are also supplied and especially, if you have a special diet regime, you may give a pre-notice and your request will be met. Also, Cha Muc is a recommended speciality when you are in Halong.