Guidlines which you can implement:

- start off the letter by greeting ur frnd, dont directly dive into the topic of holi
eg : hi disha, Its been a long time that i have written to you. I hope everyone is fine and in the pink of their health. I was so excited to write to you about the wonderful time I had celebrating holi. I hope you will enjoy and I missed u on holi, wish u were here

-Then talk about the significance of holi, why is holi celebrated

-Then talk about how it used to be in the past ( like what u have read about it, or experienced celebrating in past) and how different it was for u this year, it was so special. U can take this opportunity to site few examples of new ways or changed u saw over time wrt to holi, like water ballons filled with rose petals or plain thermacoat baloon, how ur friends tricked u into getting the splash of colors say by breaking a baloon with a pin and surprising u with the contents, say u just thought of it to b an air baloon etc., this to make it a bit interesting

-Then talk abt how u actually celebrated it
where with whome, how it started, ur frnds etc

-ten talk abt how u spent time after the actual holi game, like getting cleaned, having worn new dress and offering prayes or giving respect to elders and having a joint food and discussions u had on the dinner table

then u can tell how u fealt when u were abt to sleep, u remembered and missed ur best frnd to whome u r writing this letter, hence u took time to write this letter, and u realized holi is a good festival as u celebrated it with different ppl with diffeent religion , and it helps bring color to ur life, making it a different and spl day , and bringing in unity and enthusiasm among ppl irrespective of thier bacground

all the best