There are quite a few fish options for a nano if it's done right. Most of these fish will be sensitive to water quality, so I'd suggest taking your time and doing it slowly and cycling the tank as easy as possible.
gold dust mollys
fancy guppys Badis badis
or Scarlet Badis
just to name a few... obviously they can't all be mixed together, but these are all fish that would fit well into a 12 gallon nano. If you go through the list, find out what your LFS has in stock, and bring us some names, we can help you sort out what is compatible and how many will fit, the safest way to cycle the tank, etc...
In the meantime, set up the tank and let it run for 3 - 5 days without fish first. Are you planning to put a heater in the tank? If so, then all of the above fish will work... if not... then other than danios and white clouds, your choices would be nil. Ideally for the list above, 76 - 78 F will be a good temp. Get the tank ready for them while we help you sort it out and it will all go much faster for you.
We'll help you all we can.