Sorry for the delay.
One thing which is difficult with writing Japanese is that because it was originally written in brushes, some of the strokes are not as they seem. i.e. when writing with pens, they are still written like as if it is written in brush.
Another thing to be mindful of, is where you start writing the character (whether it is hiragana, katakana, kanji - chinese character) and the sequence of writing it. Learning and understanding that will help you understand where the next stroke leads to.
If you find a photo of penji written beautifully and want to write like that (do not use computer fonts), the best thing is to blow it up large and examine it.
The Chinese character 'ei' 永 is one character that we learn as a character which includes main strokes to write Japanese character.
But above everything, it's the balance too. This is true esecially when you are writing something that is mixture of kanji and other characters. When you write mixed kanji and hiragana, kanjis are larger than hiraganas, and some hiraganas are smaller than other hiraganas.
If anyone has any questions, please let me know I will be happy to answer as much as I can.
PS I've used ball point pens because it will be easier to see the stokes, AND it's so difficult to write beautifully in FPs.