Getting to Ziro is easy if you know how
The closest airports are Likabali and Tezpur however connectivity is erratic. It's best to fly to Guwahati (450 kms from Ziro) and proceed from there.
The closest railhead is Naharlagun (about 3 hours away from Ziro). There is an overnight train (Donyi Polo Express 15617) to Naharlagun from Guwahati. A Shatabdi is also an option but it runs only three days a week.
Ziro is 450 kms from Guwahati (Assam), about 12 hours by road depending on the weather. There are two main entry points to Arunachal Pradesh - Bandardewa Gate and Kimin Gate. (Note: All non-residents need an Inner Line Permit to enter Arunachal Pradesh. Foreigners need a Protected Area Permit)