I have had success two ways but the truth is a hard winter can kill geraniums even if you store them in a garage or shed. Most years it works to either uproot the plants if they are in the ground or move potted geraniums into a garage that is cold but not freezing. No water. You want them to go dormant. If you uproot the plants you can hang them upside down from the rafters of a garage or shed. Looks weird but due the high humidity in Western Washington during the winter they survive this way.  You can also try to place pots under an outdoor patio table that is covered with a plastic wrap to keep out wind. They need a bit of sunlight but not much as you want them to go dormant. Then every month check the soil and offer half cup of water per plant just to keep the plants alive. In April or late March move the plants to a bright window with more  heat. At this point you can cut back the plants to stumps about 8 inches tall. Fertilize when you see new leaves sprouting. Give more sunlight as the new leaves emerge. So a sun room or green house works best at this point. If you want to keep them in your garage (I did as I have no sun room) then near a window will help but be warned that lack of light and warmth will keep the geraniums dormant and ugly until May when they can go outdoors. Then it will take a month to six weeks to get them into bloom. So without a green house or sun room your overwintered geraniums will not look good until sometime in mid July....this is why I now just buy new ones each spring. But sometimes I do protect my potted geraniums under the cover of a protected patio - if the winter is mild they overwinter just fine. It is a gamble that costs nothing. It does depend on the variety - I have found the fancy leaved geraniums are not as hardy. Good luck, and remember gardening is an adventure so dig in and experiment. Maybe you'll find a better way to save your geraniums to share with us all. Keep growing, Marianne Binetti