1) Understand that getting into Medicine is a competitive process, there may be cases where you might not be accepted at Monash and hence will have to study interstate or go through the graduate entry pathway. The truth is, don't be disheartened and don't give up, if you keep trying, some day you'll be able to get in, maybe not undergraduate, but hopefully postgraduate.
2) The UMAT used to be the most important determinant in getting into Medicine at Monash, however, they introduced Late-Round interviews for High ATAR, Lower UMAT candidates. However, you need to get a UMAT around 90+, preferably 92+, in order to get in. If you get below 90, you're pretty much screwed, I think there's like one guy this year who got a UMAT below 90 in Monash Med.
3) You want a balance between the UMAT and ATAR. In a perfect world, you'd want both to be high, but the truth is, sometimes that's not possible. You have to work to maximise what your strengths and cushion your weaknesses. If you're someone who is good at the UMAT, like myself, gun the UMAT, and get a reasonably high ATAR and you have a good chance. If you're the other way around, get a reasonably UMAT, lower-mid-90s and get a really good ATAR, you'll have to get a high 99s ATAR to get an unbonded place with a low 90s UMAT.
4) Treat the interview seriously, it's not a joke. If you do badly on the interview, you won't get in, to say the least.