Intro
If you're in any doubt about whether the exterior of your home needs repainting, check the windows. Windows take a major beating from the elements and show damage and wear more quickly than other parts of the house.
Preparing windows is the same as for any other surface. Start the job in the morning, so the paint will dry by evening.
Wash the wood thoroughly with a scrub brush and mild cleaning agent (or TSP if you want to remove the gloss from the paint). Remove rotted framing members and clean mildew. Scrape loose paint and repair damaged wood. Spot-prime repaired areas and scuff-sand or degloss gloss paint. Reglaze any glass that is loose or glazing that is cracked or missing. You may have to soften the old glazing with a hair dryer, but don't use any hotter heat source -- you're likely to crack the window. Let the new glazing compound dry for about a week. Then mask off the glass at the edge of the glazing with blue painter's tape.
Prestart Checklist
Time
From 30 minutes to 1 hour for a 23-inch window, depending on the skills of the painter
Tools
3-inch tapered sash brush, putty knife, or glazier's tool
Skills
Intermediate painting skills and basic mechanical ability, careful painting and raising and lowering sashes
Prep
Wash, repair, and spot-prime surface
Materials
Glazing compound, primer, paint, masking tape