While that may sound like some cheesy military catchphrase, "Always Forward" reflects pretty well how I've been trying to apply discipline to my everyday life.
In all areas of life, we can get better, get worse, or stay the same. On our path to progress that can be seen as moving forward, backwards, or stagnating.
A simple example to illustrate that is nutrition and health. For a given meal, you can decide to eat a healthy salad (moving forward towards healthiness and fitness), some pasta or rice (stagnating), or some nasty cheese pizza (moving backwards).
Going backwards cancels out the progress made going forward. Also, in many cases, prolonged stagnation causes you to go backwards as well, because some sort of maintenance is required in that particular area. For instance, not practicing a foreign language will make you forget it.
Of course it is okay to sometimes stagnate, and even go backwards a little if it's really worth it and rare; but overall, aiming to always move forward is a great default to fulfill your goals.
The areas of life you wish to make progress on are up to you. Whether it is some project you need to work on, making money, nutrition, social skills, fitness, languages, or practicing a specific skill, it's your call. If you have many goals, prioritize, or make sure you design a lifestyle where they all fit.
Whatever it is that you want, do it every day, always forward.