There are daily departures from Nairobi’s airport to Arusha and Moshi. If you are going to Moshi, you should take the earliest shuttle from the airport, departing at 8:00 in the morning. Your first stop on the journey will be the Namanga border, where you will quickly go through immigration, get your visa, have a quick drink and proceed into Tanzania. The first stop will be at the Novotel Hotel in Arusha at 1:30. After 30 minutes, the bus will depart Arusha and will continue on for another hour to Moshi, to the Clock Tower roundabout (near Kahawa HSE), and arrive around 3:30.
Price for shuttle for tourists are
Nairobi to (or from) Arusha= $25
Nairobi to (or from) Moshi = $35
If you depart from in the afternoon from Nairobi via bus, shuttle and your destination is Moshi, you must take the shuttle to Arusha and then transfer to a bus headed to Moshi. There are countless local buses, called “dalla dalla” headed to Moshi every few minutes. Cost is around 1000 shilling (about $1).
If you are not departing from the airport, you can ask your hostel or hotel to arrange for the shuttle to pick you up.
For more details about the shuttle, and to reserve a shuttle, check out this link: