Fitness

Not with motivation, that thing is rather fleeting and unstable. Though not only forcing it with discipline, that's a rather limited resource as well.

Basically using as little discipline as possible to slowly form a habit.

So now you're going at least once a week, good work. Keep it going until it becomes a habit, few weeks to months. Once that has become a habit, add in another day and repeat the habit forming process.

It took me nearly a year to go from once a week to 5 times a week and by now during winter i can add in cardio sessions as well and up the frequency easily to 7 days a week.

As malta said, don't use motivation. In my experience and observation, motivation never lasts. If you let yourself need to feel motivated in order to work out, it will be very hard to lace up your shoes.

Discipline is a choice and it's hard, but much more dependable than motivation

Make it a habit so you don't need motivation. Set a schedule and stick to it for a month and you're set.

Workout partner. The days you feel like slacking off will be when the partner coerces you to stick to it, and vice versa

Everyone is different when it comes to motivation, but here's how I deal with it. I stay excited (most of the time) to get in the gym and see the progress I made from last time. Say last week I curled 50 for 8-7-7, can I get 9-9-9? Let's to see! I'd do the same for cardio if I did any proper cardio lol