Max your 401K, roth IRA, and HSA. Buy the whole market via index funds - check out bogleheads https://www.bogleheads.org/wiki/Three-fund_portfolio . You should be able to do all that without making any adjustments from your previous job. Keep doing that for 20+ years and you'll be set at retirement, and probably be able to retire early.

If index funds aren't your thing and you like to gamble, then you could always pick stocks too... But if you are clueless the first option is the best, and you could always add single stocks as you learn.

I had a collection agency contact me once a long time ago. It was related to car insurance. I bought a different car and switched my insurance to the new car, and they increased my rates like 2X the price. I shopped around for quote right away, and easily found a place for like 1/2 the cost. I then contacted them to cancel my insurance.

Months later they sent me a huge bill, which I refused to pay because they dragged their feet canceling the insurance. Then I got a letter from a collection agency about it. I explained that I have been a loyal customer to the insurance company for X years, and always paid my bills on time. Explained that I bought a new car and they tried to rip me off, so I found a new insurance company for 1/2 the cost they wanted from me. That I had called them right away to cancel the plan with them. That I basically refused to pay their bill because they were trying to rip me off.

I never heard from the collection agency again. My credit rating has been excellent my whole life. I'm not saying you should do this, but just sharing my one experience with a collection agency.