Sure, planning a visit to Ouarzazate, Zagora, and Merzouga promises an exciting journey offering a glimpse into the beauty of Morocco's countryside.

Best Time to Visit:
The best time to visit these areas in Morocco would be from March to May or from September to November when temperatures are moderate.

Route and Accessibility:
If you're starting from Marrakesh, you could take the route via Tizi n'Tichka to reach Ouarzazate. From Ouarzazate, drive towards east to reach Zagora. To reach Merzouga from Zagora, you have to head north first towards Rissani and then towards the east.

Altitude and Acclimatization:
While these areas do not have too high altitudes, the weather could be drastically different due to their location in the desert. Acclimatizing to the heat during the day and the chill during the night might take some getting used to.

Accommodation and Booking:
There are various options available from luxury hotels, to budget stays and camps in the desert. It is always recommended to book accommodations in advance especially during holiday seasons.

Clothing and Essentials:
During the day, lightweight clothing is recommended due to heat, however, it gets cold at night so warm clothing will also be required. Carry a hat, sunglasses, sunscreen, and water bottles to beat the heat. Comfortable footwear is a must for walking on sandy terrains.

Health and Safety:
Stay hydrated. Be sure to bring any prescription medications and a basic first aid kit. In desert areas, be wary of scorpions, snakes, and other desert fauna.

Local Etiquette and Respect:
Respect local culture and customs. Women travelers might wish to dress modestly to respect the predominant Islamic culture. Always ask for permissions before photographing people or private property.