Okay, good, 14 minutes makes a lot more sense. :)
You can improve in general, of course, but it's harder as the questions get harder. Given that you also have a very short timeframe, you may need outside help - in the form of a friend who's very good at SC (and can also teach / explain things in a clear way), or an actual teacher / tutor.
Alternatively, you may need more time.
But as soon as logical comparison, Parallelism, and Meaning Clarity join together to make my life tough, I find myself at loss
The good news is, you know where you need to work. Take a look at this:
http://www.manhattangmat.com/blog/index ... orrection/That will help you learn how to do these and how to study them. First, go back and re-try ones that you have already tried in the past, using what you learn from the above article (and the other articles that are linked in that article). When you feel that you've started to make some progress, go and test yourself on a few new ones.
Note: NOT 10+ new ones. A few at a time. Then learn from them, go back over other old ones, etc. THEN try a few more new ones. You have to make sure that you are actually learning *in between* trying new questions. You don't learn much while you're trying the new questions - the new questions are to tell you *whether* you learned anything since the last time you tried a set of questions. :)
Which brings me to my big overall point: don't follow a plan based on what might have worked for you so far - doing tons of practice questions. At the level you're at now, you've really got to be digging in and analyzing these things or you're not going to learn much more!
It's very possible that, as you do the above, you will need to go back to your MGMAT SC Guide or any other of your grammar resources - but don't just go do a comprehensive review. Rather, only go back and look at what you need to look at based on the weaknesses you uncover when analyzing a specific problem.