Positive Mental Imagery is key

There is good evidence on mental imagery and sports performance [1]. By visualizing yourself performing a certain movement before actually doing it, you can mentally practice the motor skills involved in a certain lift.
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Let’s take the squat, for example. Instead of just putting a bar on your back and lifting the weight up/down, most people can benefit from actively thinking about “how” you will squat. Visualize the way you unrack the bar, how you will go down, essentially visualizing your desired squat form.
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Visualizing how you will perform a movement will help you master the form a bit better. Since you may have improved technique when making use of mental imagery, your lifts are also more efficient and this can benefit strength performance. As an example, in a 2012 study, researchers found that mental imagery helps improve leg press performance [2].
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Now, to make the mental imagery effective, it’s a good idea to mimic the conditions you’re in when performing a task. So you can do this in between sets and/or during your warm-up to mentally prep yourself for lifting weights.
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References:
1. Richter, J., Gilbert, J. N., & Baldis, M. (2012). Maximizing strength training performance using mental imagery. Strength & Conditioning Journal, 34(5), 65-69.
2. Lebon, F., Collet, C., & Guillot, A. (2010). Benefits of motor imagery training on muscle strength. The Journal of Strength & Conditioning Research, 24(6), 1680-1687.21h