1. Don't lie. Lying on an immigration application to Canada not only is an offence, but the lie could be considered a much more serious misrepresentation leading to inadmissibility than the thing you were attempting to hide. 
  2. Very carefully consider each question before answering it. Although not lying may be the most important rule, overly broad interpretation of the questions leading to unnecessary disclosures could also get you in trouble by telling the Government of Canada things they don't need to know about. 
  3. All of the questions are semantic minefields, sometimes with no obviously right or wrong answers. For instance, under Canadian law there is a big difference between being arrested and being detained. The form only asks about arrests, and only links those arrests to "criminal offences." So you don't need to disclose detentions that didn't lead to arrest, and don't need to disclose arrests for non-criminal offences. But the legal standards you'll be judged by is how "arrest" and "criminal" is defined under Canadian law, not under the law of your country to residence or citizenship.
  4. Apply for an ETA far in advance of travel, preferably prior to purchasing an airline ticket. They're good for five years, sort of like a passport. And if you do need to answer yes to one of the questions, it may take at least days and maybe weeks to sort out your admissibility to Canada, potentially leading to significant travel delays.
  5. If in doubt, get legal advice from a Canadian lawyer. Formal legal advice is not overkill if it means the difference between being admitted to Canada for tourist, work or families reasons, and being barred from Canada subject to conducting months and maybe even years of paperwork trying to overcome refused entry.