Warm it up

As American heart association puts it: "a good warm-up before a workout dilates your blood vessels, ensuring that your muscles are well supplied with oxygen. It also raises your muscles' temperature for optimal flexibility and efficiency. By slowly raising your heart rate, the warm-up also helps minimize stress on your heart."
What that means?
It means improved strength and performance during your workout and less injury afterwards.

Your warm-up consist of two parts. Part 1 is the general routine that you should do before starting your workouts and then part 2 are warm-up sets that should be done as explained below:

Part 1: General warm-up

Start with 5 minutes of light cardio (Cycling, rowing, ...)

This will increase the body core temperature but if it's not early in the day or you feel like you won't need it, you can skip it. But we recommend that you do the cardio especially for the lower body days.

For Upper Body Workouts:

For Lower Body Workouts:

Part 2: Warm-up sets

You should do 4 sets of warm-up with a lower weight for the first exercise of each training day.
These exercises are: bench press for chest workouts, deadlift for back workouts, shoulder press for shoulder days and squats for leg days.
These sets should be as follows: (MLW: Your maximum lifting weight)

Set 1 = 10 reps @ 50% of MLW
Set 2 = 8 reps @ 50% (with a faster pace) of MLW
Set 3 = 4 reps @ 70% of MLW
Set 4 = 1 rep @ 90% of MLW