Check for smears, smudges and stains when you take your clothes off. Look at the cuffs, collar, seat, etc.
Treat stains as quickly as possible. Read the instructions on the remover.
Be aware of your environment. Some places to avoid: a wine tasting, a pig-pickin' and your local motor speedway.
Carry stain removal wipes.
Pack white items in plastic for storage or travel.
Heed the care labels on the clothes.