Ever since John Bogle created the first index fund about 50 years ago, the advice of simply put your money in, don't try to time the market, and divide between an allocation of stocks and bonds based on your risk tolerance has performed far better than anything else. This includes periods where the market has been very over-inflated. If you had the worst possible timing and put your money in around the absolute peak…
The shorter the timeframe that the money is needed, the higher the allocation to bonds. Vanguard has (in Canada) a bunch of 'all-in-one' ETFs that have as their holdings other ETFs in various asset groups: Canadian equity, US equity, international equity, bonds.
Shortly after they were announced, someone back-tested their returns to determine which of the offerings a person should get:
> I analyzed hypothetical Vanguard asset allocation ETF performance over the past 20 years ending June 2019, and here’s what I found:
> The worst 1- and 2-year periods were negative for all five ETFs.* [i.e., put it in term deposit to at least try to keep up with inflation]
> The worst 3-year period was negative for all ETFs except the Conservative Income ETF Portfolio (VCIP), which holds 80% in bonds; even still, VCIP only returned 1%.
> The worst 4-year period was negative for all ETFs except VCIP and the Conservative ETF Portfolio (VCNS) [60% bonds]. But these only returned 2.2% and 0.2% respectively.
> Looking further out:
> If you need the cash in 5–9 years, VCIP or VCNS should be the only Vanguard asset allocation ETFs on your radar. Even the Balanced ETF Portfolio (VBAL) [40% bonds], which allocates 60% to stocks, returned only 0.3% over its worst 9-year period.
> If you won’t need the cash for 10–14 years, VBAL could be an appropriate choice, as even its worst 10-year return during this period was around 2%.
> If you don’t need the cash for 15–19 years, you could look at a more aggressive ETF, like the Growth ETF Portfolio (VGRO). [20% bonds]
> If you’re investing for 20 years or more (and you are comfortable dialing up your portfolio risk to eleven), the All-Equity ETF Portfolio (VEQT) might be right up your alley. [0% bonds, 100% equities]
* https://www.canadianportfoliomanagerblog.com/choosing-your-i...
Note: if you're looking at long time-horizons (e.g., retirement in 20 years), and you can take higher risks, does not mean you have to: you need to first determine what your goal is (e.g., how big of a pot of money you need), and then work backwards from there to determine what kind of returns are needed to get there. If you need 'only' 3% returns, it probably is not necessary to take on extra risk to chase after 6%.