What's the best way to store paint for over a year?
If the can has been open, use a rubber mallet to make sure the lid is tight and sealed, flip the can upside down to further seal the lid, and put it in a cold(er) place, such as the basement. If you can remember to do that (and I never could), every couple months come back and flip the can again - may help with mixing it up later on as the paint won't be in one big lump at the bottom. Either way, you should get yourself one of those paint mixing drill bits and work it in the can for a couple of minutes when the can is finally opened. No matter how you store it, there's not way to avoid having to stir it up again before use.