i would like to do some short trips from kunming, maybe for 2-3 days. who knows some nice places which are easy to reach by train or bus?

There are so many.

The villages in the mountains near the Yangtse north of Kunming on the border of Sichuan.

Jianshui and Gejiu and Yuanyang.

Jinggu/Jingdong area.

Dali.

Luoping.

Just go to a bus stop and jump on a random bus! You won't be disappointed.

thanks a lot. do you know if there are trains to any of these villages? (dali i know there are).

Generally you want to get a bus to most destinations in Yunnan. Trains don't go to many places, leave less frequently, and the train station is a pain to get to with the traffic these days.

Once you get 'out there' a bit sometimes you need to hitch or whatever as well.

I'd recommend the north bus station on Beijing Lu (in the north part of the city) as a good jumping-off point.