Hey Varsha, Both winters and summers are good time to visit North East depending on what type of weather you like. But avoid planning during rainy season. You can reach Guwahati by train ( very well-connected to NJP). From Guwahati you can go via buses or sharing jeeps. Places you must visit In Assam : 1)Majuli Island
2)Kaziranga National Park
4) Local sight seeing of Guwahati Hope this would help you.