I see this question so much and people (both the person asking and the people answering) seem to forget the most important part - is your 4-AcO-DMT HCl or Fumarate? If you don't know, email the vendor, they'll tell you.
HCl isn't the most stable, keep it in a dark cold place like you would with anything else, make sure there is not much/any oxygen getting in if possible.
Fumarate, just store it however, as long as it's not at ridiculously hot temperatures, damp, etc, it will be fine for years.
Not sure about freebase but I've yet to see a vendor selling it, most vendors have Fumarate, and I've seen a couple with HCl.
Edit: This was an old post, I'm leaving it for the sake of history, but completely disregard my comment about storing fumarate "however" - it is pretty unstable still, so ideally an airtight baggy inside another airtight container (possibly with silica gels or something similar) in a dark cool place