I'm not sure what I would actually say to first year graduate student Bashir. This whole question is a bit like Tapestries. I think I did well as an early grad student. I managed to take in some good advice early on. I also learned a few things the hard way. Went the long way around more than a few times. I'm not sure it could have worked out otherwise. For example, not once but twice, I went out of my way to avoid learning a particular method because I just didn't like it. Guess what method I use these days? So maybe I tell first year me to hunker down and learn this method. But that involves spending less time learning other things, and working with a different set of people. Maybe I get burnt out on it. Next thing you know I'm a junior lieutenant instead of captain.
Really the only set advice that I'd give to a previous me is college me. That advice is simple, take more computer science and math classes. Pretty boring right? Well that's because I can say with some certainty that there'd be a specific pay off for doing those things. What would say I say to graduate school Bashir? Graduate school is the time of the vagueries. Obviously I did well enough. I got an alright postdoc and am at least at the point that some people are vaguely considering handing me the keys to a lab. Could it have been different/better? Maybe??
I feel like I have to include some advice. Here are a few things I went by as a newb grad student.
Read the Chronicle of Higher Education.
This advice was given to me right before starting graduate school. It seems like a pretty mundane piece of advice but it is very important. Plenty of first year students really have no idea what they've signed up for. If you have the slightest inclination to stay in academia, at an R1, SLAC, CC, anywhere. Just flip through an issue every once and a while. Your library probably has a subscription. It is useful knowledge in understanding the profession that you have signed up for.
Pay attention to what happens to those ahead of you. Especially wrt funding.
Who stays? Who goes? Who gets this job or that job? Who publishes a lot? Who never publishes? Which of the job candidates does your department hire? Which do they think are duds? It is best to resemble those who end up with the outcome that you are looking for.
"Get with a vet and track him,” he said. “Everything he does. Learn it. Copy it. Then try to outdo it.” 1
Diversify you portfolio.
It took me a while to do this. Broadening your knowledge base will make you more flexible. See my story about not being intersted in a particular method. I gave in, took a grad class, learned that it maybe it was more interesting than I'd though, and now it's about 50% of my research. Go figure.
Also, take good notes.