Digital tyre pressure gauges are inexpensive, and a useful device to own. In their absence, most track pumps are fitted with a pressure gauge and attaching the hose to the valve should provide an accurate reading. Tyre pressure can be affected by a number of variables, including rider weight (typically, higher pressures for heavier riders), weather conditions (reduced for slippery and debris-strewn winter roads, as a rule of thumb), and construction (our recent experience inclines us to believe the hype about the ability to run tubeless tyres at lower pressures).
When you’re happy the pressures are correct (typically, anything between 80psi and 120psi) check the condition of the rubber. Remove any surface debris by spinning the wheel and lightly applying a gloved hand. Inspect the sidewalls and rolling surface for cuts and nics, which can frequently provide early warning of trouble ahead. And remember: any tyre issue is easier to resolve at home with a workstand, track pump, and spares to hand, than at the side of the road.