3 ideas
Before costs, the average actively managed pound earns the market return, because all investors together are the market. Active managers charge higher fees and trade more, so after costs the average active investor must trail a low-cost index fund. The shortfall compounds every year, and the few managers who beat the market cannot be reliably identified in advance.
Build the portfolio from two distinct parts. Growth assets, mainly globally diversified equities, deliver long-term real returns. Defensive assets, mainly high-quality short-dated bonds or index-linked gilts, dampen losses when equities fall and provide liquidity. The main risk decision is the split between the two, set by your capacity, tolerance and need for risk, rather than by picking funds or timing markets.
Judge a fund and platform by everything they take from you each year: the ongoing charge, transaction costs inside the fund, platform or custody fees, dealing charges and any adviser fee. Costs are the one component of return the investor fully controls, so minimise the total rather than any single visible charge.