My first piece advice to prospective grad students would be to find a lab or an advisor that you mesh well with and are excited about working with. If you are on the same page and feel comfortable from the start, it makes all the difference. After that, trust yourself and your abilities! You are capable of more than you think.
Make your research project/thesis something you're passionate about. If you have a great idea, take it to a professor and see if you can make it into a project.
The advice or words of wisdom is simple, do whatever you think you want to do. I mean I had to really figure out if this is what I wanted to do and why. When that was settled, I did my research on programs and such but for me I talked with other academics from different disciplines. I needed to hear what it would be like emotionally and mentally and then think about how I would handle those ups and downs. Once, I had the basics of what I needed, and I knew what I could control, I put my best effort forth and then I felt content with results. This has been my mindset, to understand the coursework, to learn and adapt, and do my best. And once you’re in a program, they want you there, otherwise they wouldn’t have accepted you.
Finding your passion will take you to the right place at the end of the road. Just keep doing your best and appreciate all the opportunities provided along the way.