If you want a simple answer, consolidate by rolling all your legacy 401k accounts into a robo-advisor that handles traditional IRA accounts (ie 401k).
A robo-advisor is a tech company in the financial space. They provide one-size-fits-all opinionated investment strategy (ie they do not let you pick individual stocks etc, you respect their overall portfolio strategy) that is not actively managed (ie they buy "the market" instead of individual stocks). As a result you will be diversified and you pay extremely low fees (many company 401k plan funds have horrible fees that completely take advantage of you).
Personally, I use betterment (https://www.betterment.com/). I approve of their investment portfolio strategy (https://www.betterment.com/portfolio/) and their fees are significantly below the fund choices I have in my company's 401k, so it is a good fit for me.
The one decision betterment does allow you to make (again the goal is simplicity), is your stock/bond allocation. Allocation strategy is a bit outside of the scope of this response, but to keep things simple I'll say anything from 70% stocks/30% bonds to 80/20 stocks/bonds is probably fine.
If you have further questions, or want a more "complicated" answer, feel free to email me directly (check my profile page). I'm an engineer, not a financial adviser, but I've been actively interested in personal finance for a long time now.