Soffits, Fascia, and Trim
One of the most common areas for trim damage is wooden windowsills that rot when water sits on them. If the rot extends several inches into the sill, you'll need to replace the sill (a job for a pro). If it's superficial, try a fix. First, chip away all the rotten areas of wood with a hammer and chisel, and let the wood dry out completely (this can take days to weeks, so be sure to cover the sill with plastic in case of wet weather).
Choose a wood filler and epoxy that suits your climate conditions. Apply the epoxy as directed to seal the wood, then apply the filler to re-form the sill. Once the filler is dry, you can sand and prime/paint the repair.
Many homeowners are choosing to replace wooden soffits (the flat area under the eaves where the roof overhangs the house) and fascia (the outward-facing boards that trim the roof) with aluminum or vinyl to reduce maintenance. If you're still dealing with wood, you can fix small areas of damaged soffit panels.
First, remove any decorative pieces of wood that hold the soffit in place. Mark straight lines on the soffit on either side of the damage, from the edge of the roof to the edge of the house. Use a jigsaw to cut out the damaged piece. Nail pieces of wood, such as 2″ × 2″ or 2″ × 4″, on two opposite edges of the opening, up inside the roof and extending into the patch area, to give yourself a surface to attach the soffit patch. Cut a soffit patch '⅛-inch smaller all around than the damaged piece, and screw it into place. Caulk the seams, and then replace any decorative molding that you removed, and finish the wood to match the rest of the soffit.