How do I become a top-tier Software Engineer?

I have a CS degree from a 4 year University, but I did more fooling around than learning there. I'm now a slightly above-average engineer with 4 years of .NET web experience (mostly backend) and one year of backend experience that was more defect fixes in an old codebase than anything else.

If I wanted to be a top tier engineer, what's the best way to train myself up? Should I take online courses to shore up my somewhat-shoddy basics? If so, anyone have recommendations?

I have a family so I have some free time, but not a ton ... so I want to learn things that will have maximum impact on my career and my marketability.