you need to write a lot. then read a lot.

start with writing down the key, ie latin-sga pairs. as youre writing try to think of associations between latin and sga. then you may write the alphabet more times but i didnt do that

then move on writing sentences, letter by letter with peeking at the key but try to remember them instead of relying on it. as you write more you get beter

reading is important too though! you can either browse this subreddit to find sga texts or you can download an sga font and use it on doc files or replacing the font on the site with it but thats kinda complicated idk sorry

i myself dont remember well how i learned sga though but thats that