We may not pay attention on how much time we spend looking at smartphone or tablet. According to Statista Research Department in 2021, users in the UK spent daily on average four hours on mobile devices.
   Undoubtedly for the majority of time, while we use our smartphone, we are not taking care of our posture. Often our chin is down towards our chest and the cervical spine is flexed forward. The amount time spent in this position is enough for making our upper back adapting, changing and often originating neck soreness, stiffness, pain, triggers tension headaches. 
What we can do for improving our posture:
1
Positioning the mobile device at eyes level.
2
Limiting our time using smartphone and tablet.
3
Taking frequent breaks every 5 minutes.
4
Gently stretching neck and mobilising arms and shoulders. 

The way how we sit can impact our health and wellbeing. Often slouching on a chair for long hours may affect our way of breathing. Frontiers for young minds article is explaining what happens to our body when we slouch on a chair and how we can recognize a bad posture and attempt to find a better one.
Electronics: The Enemy of Posture and How to Protect Yourself · Frontiers for Young Minds (frontiersin.org)   

Low back pain and sciatica. National Institute for Health and Care Excellence NICE on 22 September 2020 updated guideline 59 Low back pain and sciatica in over 16s: assessment and management. Recommendation in non-invasive treatments highlight the importance of manual therapy (spinal manipulation, mobilisation and massage) with physical exercise and psychological support.
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​www.nice.org.uk/guidance/NG59/chapter/Recommendations#non-invasive-treatments-for-low-back-pain-and-sciatica

Reduce the risk of back pain episodes with a short routine exercise.
https://www.nhs.uk/live-well/exercise/10-minute-workouts/

Neural mobilization can be performed actively as exercise (see the video below)or passively performed by osteopaths, physiotherapists and manual therapists. It is very effective in the management of nerve-related low back pain, nerve-related neck and arm pain, and plantar heel pain and tarsal tunnel syndrome.
https://www.jospt.org/doi/full/10.2519/jospt.2017.7117

This review findings support that therapeutic exercise can improve posture and helping patients to decrease neck pain. 
www.sciencedirect.com/science/article/pii/S0161475417301926#f0005

Glutes exercise work is very important in order to decrease the risk of knee injury.
​https://www.ncbi.nlm.nih.gov/pubmed/29804139​