Retirement account, first. If you do well in your career/investing, then down the road you do need to start thinking about your current vs. retirement tax brackets. But in that situation, there are a variety of options. Generally, any time I can delay or avoid the govt taking a chunk of my money, I do as much as I can!
Then an after-tax brokerage account. I tend to keep funneling money into my brokerage for investing, leaving about a month of expenses in a savings/checking which provides some cushion for the unexpected. It also forces dollar-cost-averaging investing, which is the way to do it for most people.
The unfortunate thing is the lousy returns on cash and CD's. I've been 100% in equities (strictly low-cost ETF's) for a while, but after the next rate hike or two I'm going to begin gradually increasing my allocations to fixed income mutual funds....before the next recession I'd like to be about 60% fixed income, 40% equity.
If you have kids, 529's seem attractive (though I'm no expert). I have not seriously considered a rental property, mainly because it seems like to much work for a little extra return vs. the equity/debt markets....but real estate is nice diversification and inflation hedge. Except, for many people, it's the opposite with your house representing the vast majority of your savings/investment.