Toss your incandescent and fluorescent lights. Get LED bulbs (not smart lights, just white LEDs). Where applicable, install timer switches.
It’s crazy how efficient LEDs are. They are a little bit more expensive but you’ll save it on your energy bill over time and you’ll have to replace them less.
People also don’t realize how much of their energy bill is heat & air conditioning. If you don’t have pets, turn your heat off or way down while you’re at work. Just make sure it stays above freezing and above the dewpoint. If you can get any smart thermostat for cheap, they’ll save you a ton of money over the long run if you’re like me and constantly forget to set the temperature before you leave for work.
Also, thick drapes work wonders at keeping the cold out of cheap windows. You can get them and the hardware to hang them pretty cheap from goodwill. You can also wrap them in Saran wrap if you really want to keep the cold out. They sell kits, but painters tape and a cling film are way cheaper if you can hide them behind some drapes.