It depends on how you're going to use it, really.
In a sealed bottle, out of direct sunlight, at room temperature is fine for most purposes. That's great if you'll use it in six months or so.
For long-term storage, in a sealed bottle with as little air in it as possible in the freezer will work better.
I tend to purchase nic a liter at a time. I break it down into 500 ml bottles, place those in the freezer, and keep a 60 ml bottle in the fridge that I refill from the freezer bottle when it empties out. That way I'm not constantly opening and closing the 500 ml bottle.
Nic won't freeze (neither PG nor VG) so the freezer is great storage for it to slow down any chemical reactions happening in there--usually with the oxygen in the bottle.