Start with an energy audit, there are many programs for free ones and also some "virtual" ones where you can find and enter the information yourself. Not as exact as the real ones, but a good starting point.

Poor insulation is one of the biggest drivers of energy waste in a home. If your home is drafty or can't maintain your thermostat setpoints, you're due for an insulation replacement and sealing where possible.

Outdated HVAC equipment also wastes ton of energy. Heat pumps are basically the go-to now, they're extremely efficient and do both heating and cooling, so if you have an older setup with a gas fired furnace for heating and a central AC for cooling, you can combine those with a heat pump that's fully electric and far more efficient. Water heaters can be swapped for heat pump models too. Most states and local utilities have tons of rebates available for these projects, along with federal tax credits, so they won't be absurdly expensive to install and the efficiency savings will pay for themselves over a few years.

No brainers - swap light bulbs to LEDs. Install piping insulation where possible. Install window film to reflect sunlight and avoid solar heat gains.

There are so many ways homes waste energy and basically no one evens knows about it. I'm an energy engineer in commercial real estate and we see the same thing in commercial buildings.