Yeah, I want to give my opinion too, I actually started preparing from September Itself and within 1st month I did OS,DBMS & CN only, but I did a big mistake of not solving any previous year simultaneously... I plan to finish everything before my 7th Semester Exams though.
And yeah! If you put you thoroughly practice on Algo,DS and programming part you can solve any kind of questions.
Main headache is Computer Organization....
Well, majority of it is easy but some of it's questions are so tricky, to the extent that sometimes you need to formulate your own approach to solve problems, and you'll have to be extremely lucky for your hunch to be right on the day of exam.
And yes, Focusing on Maths and aptitude is like a Jackpot... Boosting your marks heavily, so don't even dream of leaving them
TOC, Compiler and Digital are all on your practice! the more you do, the better you get!