Capital Gains Tax mitigation

Hello!

I tried my hand at OTC stock this fall/winter, and I did extremely well. My question is what can I do now that the end of the year is upon us to mitigate as much of my capital gains as possible?

Currently, I'm in the process of opening and maxing out an IRA, I have a 401k with work that I could also put some of my gains in, but I didn't know if there's anything else that I could do.

Thanks!