Well, Lyra was my very first character that i made up. Before that, i had no other RP experience. I must admit, at first i wanted to make my character flawless, the perfect student who was good at everything but i found out very soon that she became boring to me so i decided to add some flaws in her character which made her alot more interesting for me and i think others too.
i mostly start with a name first. I picked Lyra because i saw the movie "golden compass" a few years ago and the name just came stuck in my mind. I used the last name Riddle by my favorite HP character, Tom Riddle (no i'm not evil

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) anyways, i used that last name because i loved that last name, simply as that and when my character meets new people she carefully explains that she only shares the same name and can not possible be related to the Dark Lord. Just like in the muggle world , alot of people have the same names. So yea, Lyra is not related.
After i found a name and last name, i think of the personality. I based my character (when i added the flaws) on my own personality. She's stubborn, curious , sneaky and doesn't mind a little chaos. But she's also kind of shy when meeting new people and veeeeeeeery bad at Arithmancy (i'm bad at math) and she's afraid that she does something wrong which leads to the result that she does mess up.
Then i look at her appearance, is she tall? has glasses? black, blonde, brown hair? and what eye colour? .. i usually go with the contrast (but not totally) of my own appearance so i gave her black wavy hair , chocolate brown eyes and a pale skin.
next comes the family history, and their bloodstatus. I used pureblood and Lyra's whole family has been in Gryffindor except for her uncle who was a Slytherin. I thought it would be interesting to have a pureblooded slytherin who's family were Gryffindors, I again based this on my own family (ok that sounded aweful haha) i look nothing like my father or mother (personality wise) but i look more like my uncle's personality.