One thing you should always do at the gym
Decent workouts need concentration, focused thoughts – distraction free is ideal. It's an oldskool description, 'getting into the training zone', but for progress 'the zone' is the best place to be. You can only get there by zipping the phone up in the gym bag, until the work is over.
There's been a few times I've carried my phone around the gym, checking it between sets. When I've trained like that, I've always felt short changed. Like I've slacked off and just gone through the motions. The training intensity doesn't reach that special place that it should. At the end of the workout the feeling of achievement is missing. It feels like the muscle rewards have been halved too.
When I've been fully focused and really trained hard, there's not much that equals that. It's very important to get to that place during your workouts. It's not only important for your muscles, it's very valuable for your mind too. Not all of us want to, or have the luxury time to sit down, close our eyes and meditate in a quiet room – but a focused workout, with the world switched off, can be just as valuable.
The one thing you should always do at the gym, is put your phone away. If you aren't already doing that, your muscles (and mind) will thank you. ;-)