If your attic is your only option for storing christmas decorations here are preventive measures you can take.
Storing christmas ornaments in attic.
With 30 years of christmas decor and a long time ornament collector.
If your attic has windows don t store your decorations near direct sunlight.
They are still holding up well.
Most artificial trees are too heavy to wrestle into a trap door attic or lug up a set of stairs.
Mostly the cheap ones.
Excessive moisture may accelerate oxidation and ruin fragile ornaments.
Check on your christmas decorations periodically.
Make sure your attic fan is up to snuff to keep it ventilated during summer.
Use hooks for garlands and wreaths.
By storing them in an airtight container they will last longer and refrain from getting musty or mildewy.
Keep ornaments away from places such as the attic or basement where there may be extreme changes in humidity and temperature.
A rolling case is a great option for easy moving.
I have a collection of old world glass ornaments i store those in a garage closet and before that in an indoor closet.
I store in the attic but some of my older glass balls have spots from our southern heat or maybe from age.