Bringing house plants in for the winter is an October ritual. Dealing with indoor pests is usually a January ritual! One reason for this is many of us crowd our one southfacing window with an many plants as we physically can. Lack of air circulation can lead to desease and pest problems, so...
#1. Try (try!) to give each plant a little breathing room, and set up an oscilating fan for a couple hours a day, especially in a tight space.
#2. Water moderately. Most house plants need a whole lot less water than you think they do, especially during the cool winter months. Experiement with your house plants and see how they respond if you let them dry out a bit more in between each watering.
#3. Examine your house plants every week. If you do spot a problem on one plant, move it away from the others and treat it right away.
#1. Scale - catch it early and you can get rid of pretty easily. Brush off the scale with an old toothbrush (as much as you can). Rinse the plant with soapy water (dish soap like Joy works great). Then swab any scale left with a Q-tip dipped in rubbing alcohol. Continue to treat until all signs of the scale are gone.
#2. Whitefly - quarentine any plant that has whitefly, because they can quickly become an infestation. Take it to a well ventillated space and wipe the underside of the leaves with rubbing alcohol. Then wash the plant with soapy water (again Joy!) Keep treating the plant in quarentine until you see no signs of the dandruff-like bugs.
#3. Aphids - Aphids can be green, pink, red, brown, white, black, yellow, or grey. You will see them in concentrated clumps and the underside of leaves. Use a spunge or a tooth brush and soapy water (Joy!) to remove the aphids. If your plant is small you can do this in your sink. If it's medium you can rinse it afterward in the shower. If it's large, layout a tarp or a drop cloth, use a step ladder to reach the top of the plant, and rinse the soap residue off with a spray bottle.