Hey! You should visit the major cities first if you haven’t been to the North-East at all. Cities like Guwahati, Kohima, Aizawl, Itanagar, and Imphal. To be honest there’s not much to see in Tripura so you can skip Agartala. But do visit these cities as they will give you a good sense of the nuances and culture of that region. It is also a good opportunity to mix with a lot of people and understand their cultural connotations and way of life. Then you can head to other remote cities and villages like Mokochung, Longwa, Majuli, Moirang, Moreh, Dzukou valley, Ziro valley, Bomdila, Tawang, etc. Be sure to visit Sela Pass during winter when it snows, as it is one of the most beautiful mountain passes in the country. If you want to you can ping me back for more recommendations and I can even make an itinerary for you if need be. :)
Hey Ashwini, Places to visit in North East : 1) Darjeeling and Sikkim tour. This is my Darjeeling And Sikkim budget itinerary : https://www.tripoto.com/trip/how-to-plan-for-darjeeling-and-sikkim-in-minimum-budget-5bacb0a591c80?ref=mobwapp&source=awp 2) Arunachal Pradesh. You can follow this itinerary of Arunachal Pradesh : Day1-Guwahati to Bomdila Day2-Bomdila sightseeing Day3-Bomdila to Tawang Day4-Tawang sightseeing Day5-Tawang to Dirang Day6-Dirang sightseeing Day7-Dirang to Itanagar Day8-Itanagar to Zero Day9-Zero sightseeing Day10-Zero to Guwahati 3) Meghalaya. There is a Government tourism office near the bus stand of Shillong. From there daily buses go to all points in Meghalaya (drop you back at Shillong in the evening). It will take 4-6 days to cover almost all Meghalaya. You just book tickets to Guwahati; from there take a sharing jeep to Shillong and stay in a hotel near the bus stand or Police bazaar of Shillong. I visited there in April 2018 so you can ask any query related to above. Happy travelling!!!!!!!!
Every state in Northeast is beautiful. The most stunning place I have ever been is Arunachal Pradesh. Do not miss Bumla Pass,Madhuri Lake,Tawaang in Arunachal Pradesj You can also go to Meghalaya. Its beautiful during and before rainy season. Meghalaya has some beautiful hiking trails. You can also go for caving in Meghalaya. Sikkim is yet another beautiful state where Yumthang,Zero Point and Gurudongmar will top my list.