Before you blow away the neighbors with your rendition of rooftop reindeer and 500 megawatts of Christmas lights, take precautions that these seasonal "improvements" don't lead to a whole series of home repairs.
There's no better place for a Yuletide heliport than the otherwise-bland top of the house. But while it might be tempting to string out lights on the roof to spell a holiday message, remember the roof was put there to repel water. The last thing it needs is to be poked full of nail holes.
Limit holiday decorating to the roof's perimeter, at the eaves and gable ends where the fascia is typically installed. These wooden trim boards offer plenty of surface area for securing light strands and other ornaments. Note that there will likely be a "drip edge" on part of the fascia, a piece of sheet metal extending down from the roof. Don't puncture this drip edge, but install any mounting hardware about an inch below it instead.
The same advice holds true for the gutters, too: Don't perforate them with screws or other hardware. There are plastic clips that easily snap onto the gutters to hold lights in place. As an alternative, the gutter mounting hardware may provide sufficient space for attaching light strings with a cable tie (those nylon "belts" with built-in "buckles").
Remember that large surface areas (like on reindeer, snowmen and plastic elves) will act like sails when the wind hits them. When shopping for ornaments like these, check the included mounting hardware. Ornaments intended for rooftop display should have beefy mounts that are able to provide wind stability. Purchase extra hardware, like perforated metal strapping and tie wires, if additional mounting security will be needed – and if you can safely improvise. If in doubt, choose a better-made display or scale back.
Up against the wall
Walls are a better choice for decorating than roofs, since they're easier to reach and less subject to weather. Attach mounting hardware to vertical surfaces, and choose locations carefully to keep water outside. Avoid placing screws or nails near joints, which could cause splitting and later lead to rotting. Wood siding shouldn't be perforated when hanging lights; use a staple or other fastener that won't penetrate the boards. Vinyl siding isn't a good bet for any kind of hardware – find an alternate location for attachment. Lights can be mounted on brick siding with steel clips that just snap in place; for heavier ornaments, use plastic expansion fittings set in predrilled holes. Expansion fittings can be used on stucco siding as well, but set them in silicone caulk.
Group ornaments on the ground prior to installing them, and work out the arrangements before climbing a ladder. Adapt decorating schemes to the house, using available posts, window moldings or other trim as safe and accessible fastening points. Nylon cable ties and twist ties are handy for making temporary connections to fences, pipes or other irregular objects.
Be creative, plan for flexibility and think about convenience, too. Maybe it's possible to permanently mount hardware (such as plastic clips or stainless steel screw eyes), and leave it in place even after removing the ornaments. That way, fasteners only have to be installed once, instead of once a year.