Like with any journey, in order to know what next step to take, you must have the end destination in mind. Making physical training choices becomes much simpler when you understand what results you want to achieve and goals you want to reach. Without that foundation you’re left to purposelessly wander, hoping for success to land in your lap, rather than deliberately planning for it.
Purpose & Longevity
It’s important that you find a purpose for why you choose to do something, but more important is finding the right purpose; which means finding a purpose that is healthy, sustainable, and effective over the long-run.
Purposes that are excessively superficial or short-sighted will likely lead to demotivation, burnout, losing interest, and a lack of consistency and discipline.
Prioritizing the long-run will allow you to remain on a path of growth and progress, while simultaneously resulting in many short and medium-run benefits such as feeling healthy, looking good, improving your posture, reducing any nagging pains, and becoming more athletic.
Extending from that long-term purpose is the ability to set effective goals in the short and medium-term. Perhaps it's losing a certain amount of fat, or improving your vertical jump, bettering your lung health, or getting rid of nagging joint pains.
Whatever it is, all that is necessary is that the goal aligns with your long-term purpose and that the goal is something you want to achieve in the near future.
It can be incredibly valuable to write out specific goals and precisely what it is you want to achieve. From there you can discover how to best reach those goals.
Measuring Your Progression
I suggest following well-known training routines, as well as keeping logs of your workouts. From this you will learn what works best for your goals and you will become more inspired from seeing the results that you created.
Knowing what exercises to choose and how to structure your workouts to effectively meet your goals can be done by asking yourself “what's the best way to reach this goal?” Doing research, asking questions, and seeking out information (most of which is free on the Internet) can be an invaluable tool.