Deciding to improve your fitness level is an excellent step toward making your life better in general, but it's much more effective if you have a fitness goal that is something that you truly want to work toward. Many people join gyms and fitness centers thinking they need to work on "fitness" to lose weight or somehow "get in shape" according to a trainer who treats the gym like boot camp, but that's not the case. It's true some people do want to exercise to increase weight loss or go through intense training to get very strong, and that is absolutely good for them. For you, however, a different goal may really motivate you to stick with your exercise program and help you find a trainer or gym that supports those goals.
Daily Activities and Strength
Fitness isn't always about being the strongest in the pack; sometimes it's about being able to get up off the floor if you stumble. It's about being able to lift a box of books without straining, or it's about being able to walk to the store and know that you're not going to be out of breath in five minutes. These fitness goals give you a particular route to follow because you'll want to work not only on muscular and cardiovascular strength but also on certain motions, such as pushing yourself up if you're on the floor.
In another corner of the fitness room is the goal of training for a specific event, like a marathon or getting ready for basic training in the military. Whether you work alone or with a trainer, you should focus on exercises that help increase the endurance and cardiovascular health you'll need, as well as the muscular strength to withstand whatever this event will throw at you.
Others just want to build muscle strength to get that boost in resting metabolism. Any trainer you work with should help you with strengthening specific muscle groups as well as improving flexibility and cardio strength. This is a fairly basic goal, which does not mean it's not worth doing, just that it might not call for a lot of specialized exercises or focus on a particular skill. Of course, if there are exercises you like and want to do more of, that's totally fine. You don't have to limit yourself to working on only one fitness goal!
Mental Health Benefits
Exercise has been found to help moderate or soothe symptoms of some forms of depression, anxiety, ADHD, and other mental and neurological conditions. This is going to be a very personal goal, and you need to find a trainer who understands that once you find exercises that you like doing, those need to remain a part of your fitness program for as long as they help you. In turn, you need to understand that if you work with a trainer, they may want you to work on opposite muscle groups in addition to whatever you have been doing in order to avoid muscle imbalance.
Fitness can be done at home, in a gym, in a class, or in another setting. Rollerskating can be fitness, weight lifting can be fitness, and so on. If you do decide to join a gym or fitness center, be clear about what your goals are and ensure the trainer who shows you what to do has experience helping others with those goals.