The best way to protect your new brass piece is to keep it in an airtight container or ziplock baggie. Oxygen causes tarnish so this storage helps with tarnish buildup!
Moisture and water droplets left to evaporate also cause tarnish to build up extremely fast. Please never wear your brass jewelry in the shower or to sleep.
Use a sunshine brass polishing cloth to remove tarnish build up, and if needed on the stud of a piercing on an earring use a sanitizer wipe with alcohol that can evaporate off of the piece quickly, being careful to avoid stones if there are any. Make sure there is NO moisture left to evaporate as this will cause brown droplet marks. Hand sanitizer on an earring post or a polishing cloth also work well to clean a brass post earring.
Sterling silver is similar in tarnish buildup from being left out in oxygen. Please store your piece in some type of airtight container or baggie to reduce tarnish buildup. Sterling is less sensitive to tarnish from sweat or water moisture, but please never wear your sterling jewelry in the ocean or swimming pool.