Judging by my reputation history the best way to reach the 50 points needed to leave comments is (perhaps unsurprisingly) to write some answers! I suggest you find some unanswered questions under tags with which you're familiar.
I actually think the system works quite well; most SO comments are worth reading. One peculiarity of the privileges that I've found is that I'm not allowed to make edits with fewer than 6 characters. I've had to leave some pretty significant typos uncorrected.
Just a point of clarification: users who can edit immediately (those over 2000 rep) can make edits of any length. The length limit is enforced for "suggested edits", which need to be approved by two other users and for which the editor earns +2 reputation.
