That's not bad advice except for the "in your nation" part. There's no point in limiting oneself to investing in stocks of just one country. In fact, it would be smarter to go with a more geographically diverse option.
Also, it's not uncommon for some lesser-known indices to be more prone to market manipulation than the most popular (US) ones.
Some could say that being local should give you more knowledge of the companies registered in your home country, but that's almost never the case for newbie investors. A knowledge of a brand is not enough, and it won't substitute for analysing financial fundamentals.