I went through precalc in school, then promptly forgot most of it once I started working. All of the bits I had learned felt rushed, so a lot of them fell out of my brain even while in school. I only had a basic understanding of most of what I "learned".

About a year ago I decided to go back to basics, and start over from zero on Khan Academy. I've been v.e.r.y slow, maybe a lesson a month on average, but have been grinding through the lowest level math to really understand and remember it. Down to addition, subtraction and multiplication even - I've relearned how to multiply small numbers in my head, and gotten much better at quick mental addition and subtraction.

I have scheduled and dedicated more time for it this year, so I hope to catch up to my original math basis. This time, hopefully, remembering all of it instead of skimming. That should set me up well for linear algebra, and then calculus next year and beyond.

One thing that may help regardless of how you choose to learn: pick a problem you want to tackle that needs Fancy Maths. It doesn't need to be anything useful, or anything difficult like "prove this unproven theorem". It will motivate you as long as it keeps your brain engaged. For me it's factoring and primality proving, where I can't even read the equations / algorithms because I don't have the basic tools. As I get further along I keep looking back to those problems and seeing how the bits I'm learning apply around the edges or to simpler factoring algorithms. It keeps me motivated to learn more to be able to dive deeper into the juicy parts.