Hold Your Phone and Tablet Properly

Find the ideal desk height and keep your feet flat on the floor when sitting (the right seat height is level with your knees).

... and more effectively, using your diaphragm. Also try breathing exercises that focus on lengthening your spine and engaging your waist muscles and lower core muscles.

... to play games that require balancing and movement. 

Playing any games while standing up is also an alternative, as sitting all day is bad for us.

... and adjust your workspace accordingly to put less strain on your spine. Ensure you’ve got a chair that supports your back and is ergonomic for your workspace.

Test your back and neck posture against a wall or check proper posture illustrations to find any areas you need to work on when standing. 

Be more aware of your feet when you’re standing and adjust your weight so it’s distributed evenly across both feet.

Besides your desk, rearview mirror, kitchen counters, pillows and mattresses are also things that influence your posture and need to be kept in mind.

... to train your body to be in the proper position, with the least amount of strain possible on your supporting muscles. But so a doctor if you have serious posture issues or pain.

Do pilates and other core strengthening exercises to help you stand taller and maintain a proper posture. 

Yoga also does that and emphasizes body awareness and balance.