Let's make sure that fitness-related activities you engage in are fun for you. That last part of the previous sentence, "for you", is very important. Playing tennis might be fun for me, but if you are not good at it or simply dislike this activity, you will do your best to simply not do it. You will go ways to avoid it, blaming either the lack of time, somewhat windy conditions, or the fact that you'd rather play singles or doubles, while the option which you prefer is not available right now and right here.
Making fitness fun will make it easier for you to work it into your daily routine. Create a list of three to five activities, which involve you moving around to an extent and which you relatively (or totally) enjoy. This way, you might, actually, start looking forward to your next fitness endeavor.
It does not need to be anything well-structured or anything what would involve locking you up in the steel-filled dungeon of a formal gym. Be open-minded and think along the lines: a fun bike ride, perhaps? Hating the traffic and not too cozy with the passing cars while on the bike? What about trail biking? Not that adventurous? What about taking your dog on a long walk or hike? Having a cat, not a dog? What about promising your four-legged furry friend to chase them around the house three times a day for five minutes? Doable, right? Your grandkid owning that lovely trampoline? Go for it and jump your heart off! Your cardio will get challenged and the impact of trampoline jumping is still a good impact, but safe enough and fun.
Weave motion-related activities into each and every day. One of my beloved clients simply walks and walks those aisles of the Safeway store - not that she has so much to buy there, but she enjoys to walk and the support of the cart gives her the reassurance she will not fall - what a great idea!
If we create negative associations with the act of exercising or moving around, they will only make it harder for us to do it. Think positively: how moving around can be fun, how you can make it fun specifically for you, which activities would be more doable than not and which ones you would stick to: both while you busy yourself with other daily tasks or do them purposefully. Exercising can be fun once we start thinking of it in the "fun" terms!