Pick a two-color scheme, if applicable. Select complements (red and green are one complementary pair, as an example) to make a splash. Use neutrals (sage and sand, for instance) for a more subdued look. Two colors of the same hue in different values (like an ultramarine blue and a pastel blue) yield contrast and an easy harmony. For a single color added to white or over the white, skip this step.
Prepare your surfaces. Scrape off all loose paint or debris with a scraper. Fill holes or gaps with exterior caulk using a caulk gun. This is important. Any loose material will, at some point, fall. When it does, it will take your new paint with it.
Paint the main section of the white house (shingles or sheathing) first if necessary. Use rollers with a heavy nap on flat areas to save time. As exteriors are often rough, you may need to go back over the areas with a brush to touch up. This holds especially for masonry. Paint textured shingles that are hard to roll with the wide brush. Use downward strokes to blend drips.
Paint the trim in the color or colors of your choice. Use the narrower brush. This gives you more control. For a single trim color, apply it to all trim, as well as shutters (if you have them) and doors and gutters if you wish. For a two-color scheme, use a darker color on the larger areas (such as garage doors) for bolder results. Go lighter for less impact. Follow the direction of the grain for wood. For gutters or shutters, follow the long horizontal or vertical direction of the object you are painting.