If you want believable characters they need to do something that has nothing to do with the action of the story. A good thing to have them do is exercise. Have them walk or run, go to the gym, yoga or spin classes.
That means making your character go for a run or walk. Most of mine walk because that’s what I do. Working out on a home gym also works. Personally, I don’t lift weights, but I do yoga and have a gazelle so that I can do the workout in my basement. That’s how I do it. I prefer to walk around outside.
My characters reflect my preferences. Since I rarely go to the gym, neither to do they, preferring to be out of doors. The theory is, if you are outside and away from home and get tired, you still have to go home. That’s the beauty of running or walking outside.
My characters are good about that. They run, walk, or workout every day. I am not always so diligent. Personally, I will go to yoga class every week, except when I’m sick. So, I do yoga when I first get out of bed, but lately that’s not every day. It should be.
My characters are better than me when it comes to their health. I do that as a way to motivate myself to be better at getting activity in on a daily basis.
If you aren’t sure what kind of activity your character can do, try the activity for yourself. Become your character taking the class or doing your workout. Then you can write about it more easily. I spent time writing down the instructions, as I remember them, that the yoga teacher gives turning the class. That way, I can create the class for my characters.
That’s the key. Try to be aware of how you feel while doing the exercise. That way you can give a realistic feel for your character’s work out or class. It’s good to make notes when you can. Make your notes as soon after the class as you can. If you need to, add to them over several classes. That’s what I did with my yoga class.
You may find that you enjoy the workout that you end up doing as your character. If so, great. If now, well, you tried it and that’s good too. This is a win-win situation. Working out doesn’t have to be a chore. It can be fun. You can have your character play baseball or basketball, tennis or any sport. If you don’t want to try the sport, go to a game. Watch others play the game. Make notes on the players, how they move and look. Research the rules of the game so your character won’t break them, or break them, if you want your character to break rules.
The point is, a realistic character should have a realistic life and do things real people do. Have them do activities. Let your characters have fun.