Where to Stay
Stay near Tha Phae Gate – there are tons of options, so do some research to see what is best for you (eg – some won’t let you stay there unless you book a trek through them). I would recommend Spicythai Backpackers. You can also find some good hostels/guesthouses with pools.
Where to Party
Chiang Mai may seem challenging at first, but it is really pretty simple. Start your night at the main party complex on Ratvithi Road, which is where you will find all the backpackers. Each night is different here, but usually Heaven Beach and Roots Rock Reggae are pretty happening. However, the complex is small enough that you can walk around and check out many different bars to see what you like. When these places close, you should go to Spicy, an after-hours club a short walk away. Great place for meeting locals, but be somewhat careful here.
Heaven Beach has a awesome live rock band every night and you can expect to hear covers of Foo Fighters, Kings of Leon, Pearl Jam, etc. Roots Rock has a live reggae band. Aside from the live music it is mostly Top 40.
During the Day
I would highly recommend going on a 3-day jungle trek (these usually also include riding elephants and taking a wooden raft down a river. Most backpackers also go to the tiger zoo, where you can play with tigers of all different sizes. Cooking classes are also popular in Chiang Mai. The street food all over the city is great as well.
Overall, the cool day activities mixed with the unique nightlife make Chiang Mai the best non-beach party city in Thailand.