How should I store leftover latex paint?
Your best bet is to transfer it to containers you can 100% fill and seal absolutely.  

It needs to be stored near room temperature, don't leave it out in the garage to freeze.  

The #1 threat on modern latex paint is mold and fungus growing in the paint. That will result in very stinky paint that is very hard to deal with (it often defies sealcoating, and will ultimately need to be removed along with all the sealcoats that didn't work). The stink is obvious after the fact, but when you're starting to paint, it can be hard to tell from the stink you expect from paint. That is why I get new latex paint for every job.

Mold and fungus now thrive in paint; they didn't before, because the allowable VOC content was high enough to make sure nothing would live in the paint can. VOCs have been pushed down to near zero to improve air quality in cities, particularly Los Angeles.