Travelling can be nerve wracking your first time alone, but for the most part it's not so bad
1. Keep any valuables on your person, (don't put laptops/cellphones/etc in checked luggage).
2. Like anywhere theft is possible, so just be aware, don't leave your bags unattended.
3. While most airports are fairly easy to use and you shouldn't have any trouble finding your way around, don't be afraid to ask for directions, or once you reach your gate ask the agents at the desk if you're at the right spot!
4. The longer flights should provide in-flight meals, although if you have long lay-overs you may find yourself hungry. Carrying small amounts of local currency (or a credit card) is useful for buying snacks/meals while in the airport. Most airports should have a currency exchanger avaliable.
5. As you depart your plane you should ask if your luggage is automatically forwarded to your connecting flight or if you have to claim it; in my experience you'll have to claim it in Vancouver and check it again for your flight to Montreal; but best to double check!
Best of luck!