Lol, I was worrying a bit about physics (I'm not great at it so I'll be doing heaps of study for physics this semester), so I checked an earlier exam - the stuff we've covered so far is roughly 3 questions out of the total 55, lol.
I was pretty 'not good at physics' going into the year too. My hint would be to learn the reasoning behind each step in the problems, rather than spending ages memorising stuff. Because you get a cheat sheet, and there isn't too much 'memorisable information', you don't really need to memorise anything. The exam questions follow a pretty predictable pattern, and so I personally found it easier to just learn the working, rather than understanding the concepts 100%
I also found it useful to have some of the working/broad steps to some of the types of problems (note: not individual problems, 'problem types'. There really are only so many of these in PHSI191) on my cheat-sheet so I could make sure I hadn't mucked up under pressure in the exam.
(Disclaimer: This is for those of you who, like me, don't have very mathematical brains. So it's a pretty imperfect strategy, and leaves you 'hung out to dry' somewhat on the harder 5% or so of questions. So if you're one of those physics-buffs who's looking at >95% in PHSI, ignore how I did it

)
I personally found the cheat-sheet very, very useful, and if your physics abilities are pretty shaky, then I'd advise getting to work on your cheat-sheet now, and learning to use it to solve problems. Do problems. Do lots of problems. You definitely learn to spot patterns in the way you solve said problems, and so get better at them.