Walk the rooms on a windy day and feel around windows, doors, and outlets on outside walls. Seal the gaps you can feel with inexpensive weather stripping or a door snake. Close curtains against strong sun in hot weather and open them for winter light. Set the thermostat on a schedule and leave it, instead of nudging it all day.
A low-flow showerhead and a slightly shorter shower reduce water and the energy used to heat it. Ask your utility whether it offers a low-cost home energy visit. Spend money on a bigger upgrade only when the payback is clear and the cushion can cover it.
Start this week
Pick one draft you can feel and block it. Then set the thermostat schedule and do not touch it for seven days.