Starting too heavy:-
The biggest mistakes in your workout program on strong lift 5×5 are starting too heavy. It does not give your body time to adapt to squatting three times a week and get stronger. You get sore and want to skip workouts instead. You miss reps and get demotivated. You think the program does not work and want to quit. Most people want to start heavy to accelerate their progress. But they usually get the opposite. If you barely get your reps on your first workout, you can not lift 2.5kg/5lb more two days later. If your legs get extremely sore for the first workout, you can not squat again two days later.
Starting heavy also shift the focus away from practicing proper form. If you struggle to get your reps early on, you will be tempted to lift with bad form so you do not fail. But this builds bad technique habits. It will make you hit a plateau or worse, get injured as the weights keep increasing. It’s not west of time to start light. Yes, lifting heavy is better. But you must learn to walk before you can run. Let your body get used to squatting three times a week first. focus on lifting with proper form while the weights are light. This work will pay off once the weight become heavy.
Strength training is a marathon, not a sprint. You do not win this game by trying to go at first as you can. It takes time to get stronger and learn proper form. And you can not gain more than 2lb of a muscle a month. The people in the gym do not care about the weights you lift. They are a focus on themselves. And they have been beginners too. If anyone laughs at you for starting light, let them laugh. 12 weeks from now, you will be squatting two plates. Their laughter will turn in to amazement.
Changing the program:-
The mistakes in your exercise -front squat instead of squats, sumo Deadlift vs Deadlift, incline Bench vs OH press, etc. Or changing the sets and reps by doing three sets of eight reps vs 5×5 to get more pump and soreness. Or doing 5×5 Deadlifts instead of 1×5. The priority of this programme is to get stronger at the big five Squat/Bench press/Deadlift/Overhead press/Row. To get strong at this exercise you have to master proper form and go heavy. To master proper form and go heavy. to master proper for you have to do the exercise a lot. To get stronger you heave to do sets of five.
Adding to much stuff:-
The usual mistake here is adding a ton of assistance exercises to hit every muscle. Especially smaller muscles that do not need much work in the first place. Some people will try to do the big five exercise in one workout. Or they do cardio 5-6x per week on top of lifting to lose fat faster. But the more stuff you do, the bigger the stress on your body, and thus the bigger the recovery need. If your muscles can not recover properly, they can not get stronger and lift more weight next workout. You miss reps. Plateau and get frustrated. Your strength and muscle mass can not increase.