There are, at this stage, no diagnostic tests in psychiatry and hence we have to work off diagnostic criteria provided by the DSM* or ICD* to try and determine the diagnosis based on a patient presenting with a constellation of symptoms. Until there is a diagnostic test for mental illness, the diagnosis and therefore treatment of mental illness will rely on psychiatrists and clinicians using their clinical acumen to help patients. That being said I believe that a number of techniques may be useful across various disorders. 

There are some basic concepts that will stand you in good stead for the future

• Help seeking and honesty 

• The Stress Bucket

• Grounding Techniques

• Self Compassion

• Mindfulness and deep breathing

• Medications- Basic advice only (speak to your doctor/pharmacist for specific information)