Ramit Sethi's I Will Teach You to be Rich is an excellent personal finance book that walks you through the different things you should think about as someone investing for retirement.
The writing style is kinda sleazy, but the actual content is dead practical and well thought out.
1) Beating the market is much more difficult than mainstream information would lead you to believe. I've been investing my money for over thirty years and couldn't agree more.
2) Matching the market is as simple as purchasing a total market index fund. Collins suggests Vanguard Total Market Index Fund (VTSAX). But that isn't available everywhere, so in my 401K I had to find the closest thing. I switched over to this about five years ago and spend almost no time thinking about it.
3) If total market exposure is too risky for ones tolerance or circumstance (I am creeping up on retirement), Collins recommends mixing in a percentage Vanguard Total Bond Market Index Fund (VBLTX).
4) Concerned about international diversification, Collins explains that is already covered through the larger US companies investing in overseas as part of their business. This comes with an advantage of a filter for the currency exchange, and the kinds of unpredictable business practices you don't expect as a US investor.
5) I have no conflict of interest in this book. I share it with anybody interested and most new grads I meet. In my experience it is sound advice for anybody that isn't investing as a profession. Even then... well, I'll let Collins describe it.
6) Lastly, this seems to be an accepted philosophy of the FIRE community. FIRE is another strategy I wish I'd had known about 30 years ago.
I maximize my 401k and IRA contributions into the associated S&P500 (SPY) and Nasdaq (QQQ) market vehicles on a regular and consistent basis. I think any broker would be acceptable (my favorite is Schwab, least favorite is E-trade). Although I prefer ETFs, at one time my corporate 401k plan only had mutual funds for investment.
The writing style is kinda sleazy, but the actual content is dead practical and well thought out.