Identify your passion and reason(s) for wanting to become a graduate student. Write them down, type it up, post it large and visibly on your desk or wherever you do your work so that it remains a constant reminder of why you are doing what you are doing and will motivate you through the hard times that every graduate student has and does go through, so that you can always see the light at the end of the tunnel.
There are so many ways to pursue your passions and interests. I'd recommend that prospective grad students be certain that they are ready for the rigour and commitment required by graduate studies. Be open to new ideas, critiques, and other ways of seeing the world. Learn from your peers, students, university staff, and the wider community, in addition to your professors. Be generous with others and build community. Don't forget where you come from.
I feel lucky to have been able to be involved in many different projects at the University of Guelph. My advice to future grad students is to get involved in as many different things as you can and to not be afraid to reach out to people. A lot of the fun in a graduate degree is being able to collaborate and work with lots of different people.
To any undergraduate student that wants to pursue graduate school, my best advice would be to study hard, celebrate your academic victories, and don't get caught up on your failures. Everybody has a story of a course they wish they did better in, or a midterm/exam that was an unexpected curveball, but as long as you learn from your past and keep pushing forward, things will work out for the better.
Although I think most prospective grad students have been told about the importance of picking a study/project that interests you, I think it's also really important to take some time to see how you interact with your supervisor and lab. These will be the people you work the closest with for the next several years, and help provide support to you in some of your toughest moments.
Do your research: on the lab, on the faculty, on the department and on the city itself. There are so many different programs/departments and it's imperative you know what you're getting into. Speak to students that are currently in the lab or have recently graduated to get an idea of how things work. There are going to be some tough times in your program and you want to make sure you're surrounded by people that want to support you and help you get through, to be successful.
I advise prospective grad students to network with as many interesting people as possible. Networking is key to finding research opportunities and gaining experiences. Even simple conversations can stimulate new ideas or help solidify original ones.
Networking is essential when considering graduate studies. I met my research advisor at an informal chemistry meet-up in Brass Taps two years prior to working for him. You'll never know when opportunities present themselves, so it's important to take chances and meet everyone you can.