Working on some simple and practical posture tips:
Simply spreading your arms (as shown in the lotus zen pose) helps open your shoulders, reset your shoulder blades, and stack your head and spine. You can then bring your arms back to normal, but keep your shoulders open. You can do this any time during the day.
Bring your portable device in front of your eyes (keeping shoulder and head posture described above), rather than your head down to your screen and slouching in.
I remember first seeing this in a TED talk or some other video, but I can’t find the link anymore. Here are some more posture tips. Let me know how that works for you.