Indeed practicing it's the key to reach your desired result. Oractuce both drawing from real life and your memory/imagination. Also, keep an eye on how your favourite artists work on proportions in their artwork. Investigate and try to understand what they wanted to tell by modifying proportions.
A classic example of this can be the David sculpture by M.A Buonarotti. His hands are huge compared to that of a teenager (and that without mention his facial features).
with this, Buonarotti wanted to talk about how strong was David, determined to defeat Goliath.
By the other hand, Comics are the best example of exaggeration, just see Matteo Scalera's work (Black Science for example).
Also, a good tip to create consistent characters, you should keep an eye on the silhouette of them. Usually we can recognise someone by his silhouette, it's like a stamp in our minds. So it's good to start character designs with some thumbnails focusing just in the silhouette. Also, doing this you will be defining the anatomy of the character, and then you can decide what you are coing to exaggerate basing on what the character is and how the character behaves.
I hope these tips to be useful. When comes to art, there is no such thing as a right solution. Do not get discouraged if the result is not fine, try to change what is not working on your drawing. You will eventually get good results if you keep on it, that is for sure always.