Find an exercise that works for you, I tend to like cycling or spinning so that’s what I’ve stuck to, and schedule recurring time to do it (ideally on a calendar that beeps at you, i.e., your phone). Until I scheduled time to exercise regularly I never remembered to do it. I’m also extremely calendar driven, so if something isn’t in my calendar it may as well not exist in my world.
I’ve also heard of people having success with setting an arbitrary personal rule — like not showering at home and only showering at the gym. Then once you’re there, just do something small like walk on treadmill for a few minutes, and maybe you’ll catch a groove and decide to continue.
If you decide you want to lift at a gym, I found it super helpful to have some sessions with a personal trainer to put together some workout sets that you can cycle through. If you don’t have the money or don’t want to get a trainer, there are tons of forums out there and well used and liked workout programs that you can follow. Google is your friend here.
Consistency is key! Find something that motivates you and take advantage of it!