Font structure is the fundamental problem that puzzles calligraphy lovers! So, how can we master the font structure? As you said, you don't know which word is longer or shorter. My personal opinion is that you should study the standard font structure first and distinguish it carefully. For example, the happy word "Xing", the font structure of printed fonts is the most reasonable. You should see that the lower horizontal of Xing's local character is the longest in the whole character, and then the lower horizontal is longer. . . .
In fact, the font structure is simply a key issue. You should focus on the characteristics of printed fonts and find out the key points of each word, so as to grasp the font structure! ! Then you take the time to think about the handling of glyphs in calligraphy and their integration. I believe you will be able to master the characteristics of glyphs quickly! ! !
I hope my answer can help you practice your handwriting! ! !