Work Hard in College
One really needs an excellent (not just good or great, I mean excellent) GPA to get into a reputable international grad school. It is not just helpful, but absolutely essential to target a perfect 4.0 if one plans to move up about a thousand places in the rankings and get admitted to grad schools like MIT or Stanford. One needs recommendation letters that say things like, “He’s the best student I have ever seen.”
If your undergraduate degree was not obtained from a top-ranked college, it is necessary to convince highly ranked graduate schools that the university you got your undergraduate degree from was way, way too easy for you. Doing this is only possible if you have consistently outstanding grades.
Don’t Waste Time doing Extra-curricular Activities
Unless they include research in a field related to your major with a professor or at a research lab, I don’t think extra-curricular activities increase your chances of getting into a good graduate school. In other words, if you want are applying for a doctorate in physics, having been part of model united nations clubs or religio-political student associations in your undergrad years won’t really help you much.
On top of that, taking part in an unnecessarily large amount of extra curricular activities can make students lose focus in their studies, resulting in lower GPAs.
Once Again, The Internet is Your Friend
I listed several helpful educational resources on the internet in my previous posts. Here are some more:
Ask Other Physicists
The biggest advantage of having an internet connection and access to science-related forums like the one I mentioned above is that you can discuss your problems with physicists around the world and listen to their advice. Often it turns out that they have been through similar problems and/or know a good solution.
Ask yourself why you want to become a physicist in the first place. If it is for fame or money, then I don’t think physics is the right career for you. At any rate, I don’t think that’s the right attitude. Get a PhD in Physics only if you are genuinely passionate about it and want to make your own contribution to human knowledge and know more about the world.
Also, get rid of your ego. You don’t have to be right all the time. Sometimes it is far more noble to accept your mistakes, learn from them and move forward. That’s what science is all about.