If you're serious about lettering and typography, you may have heard of the term "overshoot." If you haven't heard of it, take notes because it's a small detail that can make a world of difference.
I went over the basic principles of alignment in this post. So you should know that the bottoms of letters generally sit on the baseline and the tops either hit the x-height if they're lowercase or cap-height if they're uppercase (don't worry about ascenders and descenders right now).
There are some instances when you want to ever so slightly extend parts of certain letters above or below those guidelines...that's called overshoot. Even though those characters are aligned with the other letters, your eye will actually perceive that they're shorter or smaller. This is because only a tiny portion of those particular letters are hitting those invisible guidelines.
Take the letter E for example. The top and bottom strokes are both adjacent to the cap-height and baseline. In contrast, if you look at the letter O, only a small portion of the top and bottom touch the cap-height and baseline.
The special cases where you want to use overshoot are on rounded parts of letters like C, O and S. You'll also want to overshoot the pointed parts of letters like A, M and V because the same issue occurs: There isn't a significant portion of the letter touching the invisible guidelines. This principle is not only limited to capital letters. Be sure to use it on lowercase letters too.
The key thing to remember is not to overshoot too much. You want to extend the characters just enough so they appear similar in size to the surrounding characters. Though not all styles of type require this adjustment, many of the classic sans-serif and serif styles need it. It's a tiny modification that will help your letters have a more balanced look and feel.