When weight training there a few things that are important to remember. Some people when they go in the gym just sling weights around and don't think about what they're doing. There's more to working out than just picking up and putting down weights. You have to really focus on the contractions and squeezing at the top of your lifts. Mind muscle connection is so important because it's what really helps you build muscle. You can't go into the gym and just lift without thinking about what you're doing. Really focusing and thinking is a big part of working out, it's tough to establish at first so I would recommend dropping the weight until you get it down. Another thing that's very important is to mix up your workouts. Every other week or every two weeks you need to change the reps your doing. Most people will do 6-8 reps on every lift for a week and then change to high volume hitting between 12-15 reps for the following week. Doing this will keep you from hitting a plateau so you can continue to build muscle. Not only should you change the range of your reps but you should be doing different workouts every time you go. Your chest day shouldn't be the same every day nor should any day. Constantly be thinking of different things to do when you're training whether its free weights, machines, or cables. There's a lot more involved in working out than just lifting weights, you should be using your brain too. Now let's get to work, and use mind muscle connection.