My geraniums have reached now their 8th birthday.

There are a number of ways to do it....from taking inside to a good window and keep them going there for as long as possible.
Or, cut them up into cuttings and pot them up.

Or, the preferred way of mine...remove them from their soil BEFORE any hint of frost touches them. A frozen geranium is a lost geranium.

Into the cool, dark and very dry environment, you place the plants --either hanging upside down or leave them in their pots and place them on a shelf to thoroughly dry out.
No water, no light, no heat, should touch them.
They have to be kept dry.

Don't cut them back at this time.

In mid February, bring them out to a place you have put many, many newspapers ...to catch the debris. Remove all the old soil from around the roots. Remove all the dead leaves and remove all the damaged stems.
Cut them back by 1/2....1/3....generally to about 4" to 6".

Inspect the roots for any sign of damage there and remove if necessary.

Gather your potting soil, mix in some peat moss and builder's sand, put some shards into the bottom of a pot that has drainage holes, then add your potting soil mix.
Make a hole in the center and put your plant in; firm it up and give it a good watering....until it drains.

Then into the best window...north will not do...
Do not water again until new leaves begin to form.
Don't fertilize until new leaves form, then feed at about 1/4 rate until the plant produces much foliage...then increase fertilizer as is called for.

In about 4 weeks you should have a good supply of new leaves form....and in about 2 months, maybe...new flower buds. But don't be disappointed if the flower buds don't form as fast as you'd like.
That can depend on just how much sunlight you give it.

At the window, turn the plants 1/4 turn every day...or so.
This gives all sides of the plant equal amount of sunlight.

This is proceeded with until its time to put them outside again...pot, bed or container.

The key to this method is ...no moisture should touch them while in storage...after all, what is that for?
No light...that could initiate growth...growth to what?
No warmth...that also could initiate growth.

Keep the temperature below 55...above 35.

Never put these plants into plastic either...the container must breathe...the paper bag is such that allows that very well....but don't close it.

I have had my own Pelargoniums for three years and have managed to keep all but 2 plants alive every year by putting them in my windowsills during the winter, even though my only available sills are east-facing and drafty. They did get leggy, but they were all ok. This winter though I'll have to move them all to the basement with grow-lights because I have more now, and the older ones are bigger now--too big for my windowsills. I am not even going to mess with cutting them or anything. I'm just going to let them keep going.