The only advice I have is to practice. When I was on the IChO olympiad website for this year's olympiad 4 months ago I found the questions in the pdf below (from the website) quite useful, some are quite easy but most are quite hard (for me anyway!) and require a lot of thinking.
The website is here
Also she/he will need to practice experiental techniques. Hopefully your friend will go on a special course thing in Canada to prepare for the finals, as they do in the UK.
I'm hoping Canada does really well in the IChO this year!