While you're learning the metric system, be aware of what you're measuring. Feet and meters, for example, are units of length. Grams and pounds are mass. Ounces, liters and gallons are liquid measures of volume. Acres, square feet, square meters and hectares are units of area. Seconds are time in both metric and English systems.
Many disciplines have their own units. Some of these, like the pharmacist's drams and grains, evolved over hundreds of years. Be aware that unit systems you take for granted have metric equivalents.
Decimalization is a big advantage of the metric system. All units are based on a few base unit names. To make them bigger or smaller, you multiply and divide by powers of 10. Greek prefixes were adopted to make them easier to use in everyday language. So .001 x a meter is a millimeter, 1000 x a meter is a kilometer, and so on. The most common prefixes used are micro, milli, kilo and mega, to describe millionths, thousandths, thousands and millions. People use other prefixes, such as deca and centi, though not as often. Practicing these prefixes and their meanings will help a lot in learning the metric system.
Museums will encourage patrons to learn metric units. A good science museum, in particular, will have a display explaining how to use the different units. Displays and literature will use metric prominently and exclusively.
Look for the use of the metric system in your workplace. If you're an electrician, for example, you're surrounded by amperes, watts and volts, all good metric units. If you're a mechanic, you probably deal with both inches and millimeters. If you work outside of science, engineering or technology, you probably deal with English units. Be aware that your counterparts in other countries will use metric.
If you take any "hard science" class, such as physics, chemistry or biology, you'll be using grams, meters and liters exclusively. Here, the odd conversions of the English system---four quarts to a gallon, 12 inches to a foot---are a potential source of errors.
When you shop for everyday needs, pay attention to the labels. Most packaging now gives weights and volumes in both English and metric. You can get a feel for how different units are used and how they compare.
You won't see miles, gallons, or feet outside the U.S. borders, unless you're in Liberia or Myanmar. Road distances will be in kilometers, the gas pump will measure liters, and the bank signs will show the temperature in centigrade.