Build the mathematically optimal portfolio using Modern Portfolio Theory. The Efficient Frontier shows every risk/return trade-off — find the allocation that maximises your Sharpe ratio, minimises volatility, or targets a specific return. The same approach used by institutional fund managers.
Every point on the Efficient Frontier represents the highest possible expected return for a given level of risk (volatility). Portfolios below the frontier are suboptimal — you're accepting more risk than necessary for a given return. The goal is always to be on or as close as possible to the frontier.
The Sharpe ratio = (Portfolio Return − Risk-Free Rate) / Portfolio Volatility. It measures how much return you earn per unit of risk. The "tangent portfolio" — where the Capital Market Line touches the Efficient Frontier — is the portfolio with the maximum Sharpe ratio. This is typically the optimal mix for most investors.
Holding assets that don't move in perfect lockstep reduces portfolio volatility without necessarily reducing expected returns. This is the only "free lunch" in finance. Low or negative correlation between your holdings is the key driver of the Efficient Frontier's curvature — the more diversified, the further left the frontier extends.