So the best way to avoid a hangover is to not drink alcohol, or stick to a limit of 2 drinks in an evening (regular evening drinks) or 4 drinks in an evening (social occasion).
Otherwise some of these tips may be helpful at reducing your hangover.
(No I can not issue Medical Certificates for hangovers.)
Stay hydrated before, during and after drinking, drink plenty of water after finishing drinking alcohol or use Powerade, Gatorade or Hydralyte to help with the salts lost during drinking.
If you have an upset stomach (not nausea/vomiting) or reflux (GORD) from drinking you may find taking Nexium before you start helpful, as it reduces stomach acid, so your stomach may be less irritated by having less acid present and you should get less burning from reflux.
Nurofen (ibuprofen) is a better option for pain relief the next morning rather than Panadol (paracetamol), as long as you rehydrated yourself and you have no contraindication (reasons you shouldn't take ibuprofen). You have given your liver a pretty good workout breaking down and removing alcohol and your liver will also have to work on breaking down and removing the paracetamol.
Lastly try taking a multivitamin on going to bed, you have lost (peed out) a lot of vitamins during drinking, so replacing them can help reduce that morning hangover.
If drinking is a problem for you or someone you know, it might be time to talk to a professional, speak to your doctor or visit www.alcohol.gov.au for helpline numbers in your state or territory.