Clothing made from all-natural fibres will shrink if washed in hot water and tumble-dried. To avoid shrinkage, wash the article in cold water, then either lay it flat to dry, or hang it over a banister, etc.
Clothing made from polyester will not shirnk, no matter how you wash it. It's safe to wash a fleece jacket/sweatshirt in hot water and then tumble dry it.