Walking is the best way to feel the pulse of the capital. Since Kohima is on a hill ridge, you almost always travel up or down. Public Bus Transport is cheap and frequency is good to get around main town. Otherwise, there are Taxis available with minimum charge 80 INR.
You can always go for a picnic/trekking in the forest. There are rivers where you can picnic and the forest are really beautiful. You can find different varieties of orchids which you will never find anywhere else in the world. Whether it is during winter or spring the sight of the forest is breathtaking.