The first mistake you can make as a freshman undergrad is taking too many credits. 17 is bordering on too many. I would recommend starting with 14-15 if you come from a strong HS background (all AP courses in last 2 years, 4-5 on all exams or prep program with good track record) and 12-13 if you have a weaker background (underfunded school, few AP/IB courses).
There is absolutely no reason to take more than 15 credits in your very first semester at university. Do not sabotage yourself. Undergrad (and being a pre-med in general) is a marathon, not a sprint. Don't believe me? Search for the umpteen billion threads on SDN through the years titled something like "OMG tanked first semester, how to recover?", "Will 5 Ws in two semesters hurt me???", "Bad freshman year, is this a good upward trend??". It's better to underestimate your own potential and get straight As than to go hard in the paint your first semester and make straight Bs (or even, gasp, a C!).
My second piece of advice is that "how many hours" is the wrong question to be asking (another generic rule for being a pre-med, if you are asking 'how many hours?' you aren't thinking hard enough about what you should be doing). There are two pieces of ultimately very helpful information you can obtain about a class from the moment it starts: A) the syllabus, and B) advice from people who took the same class with the same professor in the past and did well. The syllabus tells you what the class covers and how grades work, with the latter being far more important. Take professors with more lenient grading policies and opportunities for extra credit, retakes, dropped exams, and finals you can either opt or top out of (i.e. nobody with a grade > 94 needs to take the final, etc.). You can't bomb an exam if you don't take it (think about it). Ask students who did well how they studied and what materials/resources were the most useful for preparing for exams. Every class is different. A lot of the O-Chem resources people swear by on the internet, for example, did bugger-all for me in my class because the focus of the exams was just radically different from what is typical.
My freshman English professor had a saying about coming to a class or event several weeks ahead: "Start walking now!". What he meant is that you should not procrastinate and cram. This is good advice. At the same time, it is incredibly difficult to follow because most 17-18 yr olds are absolutely horrible at time management (I was), undergrad gives you more freedom than youve ever had before in your entire life, and it is entirely possible to leave everything until the very last minute and still do well in undergrad if you're bright enough and like to drink coffee. My number one source of anxiety as a freshman pre-med was feeling that I should always be working. This feeling is ultimately more crippling than motivating. The way to fight it off and get everything done is to plan, plan, plan. Set out the activities you want to accomplish that day, check them off as you go, and when you're done for the day, BE DONE for the day. Go do something else. Yoga, football, browse memes, watch movies, read, hang out with your friends, w,e but have a life.
Finally, when you inevitably bomb an exam (and you will) don't wallow in your own pity about it. Don't spend time worrying about whether or not you deserve to be in uni or if you're a fraud or something (and you will feel that way a lot of the time). Be proactive and use all of the resources at your proposal: classmates, learning center, office hours, the internet. Figure out what you need to do better. Often, all it takes to figure this out is literally asking the professor, "I'm having a hard time doing well on exams even though I feel prepared beforehand. Can you offer any advice on improving?"
