How do the benefits differ? What would you owe in out-of-pocket costs if you were to be injured or get seriously ill? How does that compare with your out-of-pocket exposure on the employer-sponsored plan? Are your doctors in the network of the individual plan? You'll want to carefully consider all of these things before switching, and keep in mind that you won't be able to rejoin your employer's plan until the next open enrollment window offered by your employer.
A good place to start is HealthCare.gov. This is the health insurance exchange created by the The Patient Protection and Affordable Care Act, and is a one-stop shop for private individual market health insurance plans (note that the exchange itself is run by the government, but the health plans for sale in the exchange are all private, from the health insurance companies with which you're already familiar). People in 39 states use HealthCare.gov to enroll in individual market plans. The other 11 states and the District of Columbia have state-run exchanges, and you'll be directed to their sites from HealthCare.gov when you select your state.