If you're new to the gym, there are some key mistakes and pitfalls that can sabotage your progress. Don't worry too much as even the most experienced gym-goers are guilty of some of these.
We understand that getting starting in the gym can often feel like information overload, especially with everybody having their own 'perfect formula'.
That being said, here are a few things to watch out for:

Staying properly hydrated is going to help your performance in the gym, reduce risk of injury and help with recovery outside of your workouts as well.
We need to fuel our performance in the gym accordingly. This isn’t just about what you eat immediately before you workout, this is about making sure that you’re giving your body the nutrients it needs to not only fuel your workouts but also to fuel the rest of your day, fuel your recovering and stay healthy.
This is very individual but focus on eating enough food overall and aim to get a wide variety of nutritious proteins, fats and carbohydrates.

The most common offenders here are things like barbell squats, deadlifts, bench presses, etc. Whilst there is absolutely nothing wrong with these exercises, as they are great exercises where you get a lot of bang-for-your-buck, these exercises are not absolutely essential when someone is first starting out.
You can hit the same muscles with many other exercises and arguably these might be less technical and easier to learn, they require less equipment and might suit the person’s anatomy better.
This one isn’t just for new gym-goers, these is a common pitfall for experienced people too. Most injuries happen when people go too heavy too quickly. Even if you have great technique, pushing things a bit too far, too soon and exceeding your current capabilities will normally result in inconsistent technique and potentially lead to little niggles and potentially injuries that might mean you’re forced to scale things back. We would encourage everyone to play the long game and err on the side of caution.

Obviously you will burn a lot of calories in the gym, depending on the type of exercise you do… but we try to encourage people to see the gym as where they create a stimulus which then causes us to get fitter/stronger/bigger/etc whatever your goal may be.
If someone’s goal is to get into better shape and maybe loose a little bit of weight, then we then encourage them to focus on lifestyle factors outside of the gym and nutrition to be their main method of creating an energy deficit.
Meaning, that in the gym - focus on getting stronger and getting fitter. Outside of the gym, focus on your nutrition and activity to create any calorie deficit/surplus you may need to achieve your goals.

Cardiovascular training is an important part of any training programme but too much can often be counter-productive, especially if you are letting it get in the way of your strength training. We would encourage strength training to be the cornerstone of your training programme, as this will help us build a more robust, stronger physique with more lean tissue on it. This will provide a stable base for you to add in any cardiovascular on top of that.
Not only will this keep your training fresh mentally but occasionally having some variety in your workouts will actually help to avoid plateauing physically. Of course if we vary our workouts too much then you will struggle to make consistent results but you need to keep certain aspects of your training fresh, so you don’t get bored.
People often try too hard to make their training ‘optimal’ and completely overlook the enjoyment factor. Whether this is the form of exercise they choose, the environment they do it in or who they do it with. Often finding a form of exercise that people enjoy will lead to better consistency and compliance, which will leads to better results long term over choosing something more ‘optimal’ that they will never be able to do consistently because they don’t enjoy it.

If exercise in the gym is the stimulus, then the adaptation we are trying to drive happens when we are in fact outside of the gym, i.e. you don’t actually get stronger/fitter/grow muscle whilst you’re training… you in fact do that when you’re outside of the gym at rest. So alongside proper hydration, good nutrition and good quality sleep, having enough rest or days off is essential to making progress!