Interestingly, you can copy traders on sites like eToro. So every investment they make is copied by whatever investment you make in them (if you invest $1000 in the copy and they have $10,000 in their account you will buy $10 of a stock if they buy $100). You can search for traders based on their past performance. The problem with this is that you expose yourself to survivorship bias. Out of the large number of investments, some have inevitably just struck it lucky when in fact they have no idea what they are doing.
But the effect of this, if copying become really popular, could make for interesting implications.
Just maintain your current asset allocation, keeping in mind that you should be very slowly moving things out of equities and into fixed income as you age. If you’ve been maintaining the same ratio of stocks to bonds for years and you’re planning on radically shifting that upon hitting retirement, instead just start shifting to somewhere in between now. Make a plan for your asset allocation strategy as you age, and only modify that plan based on your own risk tolerance changes, not based on how the market is doing - you use the plan the rebalance your portfolio based on what happens in the market. By sticking to an asset allocation plan, you will naturally buy low and sell high, and it requires absolutely no attempt at predicting where the market is headed.
Keep in mind that you don’t need all your money right when you retire. If you’re holding half in stock and the market falls in half, you’re only down 25%, you can sell some of the bonds to rebalance and provide you cash for living and maybe buy a few cheap stocks, and then have the stocks recover by the time you need to liquidate the rest of your portfolio. Only if you need all of the money you’re saving in the next few years should you be extremely conservative and put it all into bonds and money markets, and this will normally only be true if you’re for instance saving for a down payment on a house that you absolutely want within the next couple years, or saving for college where you know exactly when the money needs to be ready by. Saving for retirement you’ll generally have way more money than you’ll be spending in a single year (since you’re going to need it the rest of your life) and so you can weather the stock storm on a decent portion of your portfolio as long as a good chunk of it is safe.