The two most common sources of microplastics that enter your body are from the vessels you eat/drink from, and from particles in the air from things like clothes, carpets, furniture, linens.

How to avoid? Use stainless steel, aluminum, copper, (or other metals), ceramic, or glass storage vessels for things like water (including your Brita) for warming things in the microwave, or for storing food, and reduce buying things in plastic if you plan on keeping them there for awhile (eg glass ketchup bottle). Replace any plastic water pipes in your wall with good ol copper. My main water vessels are all stainless steel.

For particulate, consider air filtration, buy clothes/furniture/carpets made from natural animal/ sources like cotton, wool, bamboo, avoiding plastics like polyester. That includes your scrubbing utensil for dishes. Your carpets are probably made with some sort of plastic, so if it's too much to do hardwood, or replace with a natural fibre, the Dyson vacuums are good at getting out loose microplastics.

Be warned, one time I almost bought a stainless steel cup from a reputable retailer, and upon further investigation it was just plastic with a steel coating.. Yep, made in Communist China..