I wish I had applied to more schools. I only applied to 3 because their locations and programs most suited me. 2 (McGill and UBC) are quite selective, and although I haven't heard from them, I was rejected from Simon Fraser, which I take as a bad omen... I hesitated to apply anywhere else because it seemed like a waste of resources when I knew (for personal reasons) that I wanted to be in Vancouver or Montreal. I didn't realize at the time that I would rather be in a school in another city where I have fewer (or no) friends and family rather than fighting for paid work in Vancouver or Montreal... So in short I wish I hadn't let personal rather than academic considerations determine my application process. Not that personal considerations aren't important... Just that they shouldn't be overriding concerns.
I also wish I had spent more time on my Simon Fraser application and had it edited by other people, like I did my statements for UBC and McGill. My gpa was higher than SFU's average and I have very good LsOR and internships in NYC, so I didn't spend as much time on their personal statement as I did on the one for UBC and McGill, where I am a more "average" or "below average" applicant. Big oversight and overconfidence that I guess contributed to my rejection