Just after 4 a.m. on a recent Friday, while most of the neighbors in her leafy Boston suburb were still asleep, Jennifer Guidry was in the driveway of her rental apartment, her blond hair pulled back in a tidy French braid, vacuuming the inside of her car. The early-bird routine is a strategy that Ms. Guidry, a Navy veteran and former accountant, uses to mitigate the uncertainty of working in what’s known as the sharing economy.

Ms. Guidry, 35, earns money by using her own car to ferry around strangers for Uber, Lyft and Sidecar, ride services that let people summon drivers on demand via apps. She also assembles furniture and tends gardens for clients who find her on TaskRabbit, an online marketplace for chores.

Her goal is to earn at least $25 an hour, on average. Raising three children with her longtime partner, Jeffrey Bradbury, she depends on the income to help cover her family’s food and rent. That has become more unpredictable of late. Uber and Lyft, her driving mainstays, recently cut certain passenger fares. Last month, TaskRabbit overhauled the way its users select their helpers; immediately after the change, Ms. Guidry’s stream of new clients dried up.

“You don’t know day to day,” she said. “It’s very up in the air.”

In the promising parlance of the sharing economy, whose sites and apps connect people seeking services with sellers of those services, Ms. Guidry is a microentrepreneur. That is, an independent contractor who earns money by providing her skills, time or property to consumers in search of a lift, a room to sleep in, a dry-cleaning pickup, a chef, an organizer of closets.