Always give 100% concentration
Warming up allows you to loosen up your muscles and prepare you mentally and physically for the heavier upcoming sets. But what is too much, and what is too little? So how do we warm up properly for lifting weights? There is no one size fits all method when it comes to warming up, but there is one thing you should keep in mind. Your warmup should be done with the least amount of repetitions, and the least amount of sets to get the job done.
Always give 100% concentration to every repetition of every set when warming up. Warming up shouldn't be a time when you talk to your friends, or think about what you are going to be doing on the weekend. If you put all of your focus into your working sets, then why wouldn't you do the same with your warm up?
Here is an example of a warm up for bench press. Let's say that your working sets are with 205lb for 4-6 repetitions.
95lb - 6 repetitions.
135lb - 6 repetitions.
160lb - 4 repetitions.
185lb - 2 repetitions.
195lb - 1 repetition.
This is only one example, and as previously stated there is no one size fits all. Start somewhere and then you can make adjustments as you gain perspective. Keep in mind that warm up sets are only for warming up. You want to never fully exert yourself during warmup. Doing this allows you to put the most amount of intensity into your working sets, which have a much higher priority. When you lift weights, you are either lifting to warm up or build muscle, there is no in between.
It is actually easier for injury to occur working with lighter weight because many times the lifter will take that weight for granted. Don't let that lifter be you! Overall you want your warm up to be based upon feel, and like many aspects of bodybuilding and training, it is going to take some time to determine what feels best for you. Save the heavy sets for stimulating muscle growth, keep the warm up sets to the least amount of sets and repetitions as possible, and strive to improve upon these factors every time you step into the gym.