How to make good OCs for dummies

Tip #1: Character Profiling - Species and Relationships

Well, first of all, I am aware that some Oc creators may have an inability to draw nicely. Which is totally fine. Not every Oc needs an illustration to describe its character. So, I decided to start off with character profiling, an important process needed to be made when making a proper original character.

Species
When it comes to mary sues or overall terrible Ocs, I seem to notice their terrible choices of species. And what I mean by that, is that they choose too much species for their character to be. In order to not screw this up, it's best that you know what fandom your character is coming from and what species the other characters may be. For example, I've seen someone make a Breadwinners oc with their character represented as an alicorn and duckling species. Another terrible one I've seen is San's supposed "girlfriend" with the species to be skeleton, neko, unicorn, and some other sorts of breeds. Choosing multiple species for your character isn't exactly a good idea, unless your character comes from a universe where there is more than one breed present (especially in a sci-fi, mythical, or supernatural genre). But, however, it's best to have at least two breeds for one character. Meaning, having the species at least half something and half something. An example for this if if I were to make a half human, half vampire OC for Jojo because it's proven that a human and vampire can make love in terms of Dio and his birth to Giorno. (But that's actually not a good idea, don't do it unless you know you can arrange it well :^)) Overall, it's best to just keep it at one species. If you make a MLP character and decide to make it a unicorn or whatever, I suggest you keep it that way and don't, I repeat, don't make your character an alicorn unless you know how to arrange it well. Same goes for any other fandom. Alicorns are way too OP and will possibly ruin your whole character because of that fact.
(Romantic) Relationships
Here's another big problem we see with Ocs. Many people would argue to me about how many people make OCs just to have a character connect to their favorite canon characters, which I do too actually. You just have to know how to do it right. Some original characters shipped with canon characters can turn out fairly decent, but you have to remember that the event happening is very unlikely. And, in order to make it believable, you have to make sure not to break the canon character's character and personality. I've seen this many times with Izaya Orihara, who is definitely way too strange to ever get a romantic relationship with anyone. He likes humans equally, so making him choose a "favorite" is way too unlikely. Try not to character bash other characters in the storyline just to have some room for your character either. It just ruins the whole plot. I believe seeing this issue before in a Black Star x OC where Tsubaki was bullying the character. Obviously, that is not accurate. Tsubaki is not the type of person to act that rash. In fact, she is depicted as a very shy and kind character. When making romantic relationships between your character and a canon character, also remember to make a reasonable way or some sort of description on how they would end up that way. In my opinion, the best way to go is through some sort of unrequited love. In simpler terms, have your character become somehow infatuated with the canon character. But, do not make the canon character like your character unless there's a good reason behind it and when I say "good reason", I don't mean "My character is very lovable and sexy" or anything of that sort.
(Friendly) Relationships
Some characters tend to go overboard with the whole concept of friendships and will sometimes end up making everyone befriend their character. Relationships go along with personality. Remember that not everyone will necessarily have a liking to your character. Some canon characters will have certain pet peeves and stubborn or cold personalities that will lead them to not like your character. Just try to keep your friendships stable with canon characters and make sure the friendships are believable. For example, if you have your character become friends with Jotaro Kujo, you have to remember his personality is very cold and almost emotionless. It's possible to make him care about your character, but he can't be too crazy about it. You can't make him suddenly cheerful and happy just because your character is friends with him. He has to remain the same without change unless you feel the need to give him a short length of character development like showing him how he cares more than he seems or something like that.
Rivalry (Relationships)
I don't see this problem as much, but sometimes it goes along with character bashing and romantic relationships. I can imagine seeing someone making a potential love interest for a canon character become their enemy just because they are either dating or have an interest in that canon character too. Now, obviously, it makes sense if the potential love interest character actually likes the character being shipped with yours. But, in other cases, creators will character bash the potential love interest unknown to the connection between them and the character you desire to be shipped with yours. This sometimes happens with characters that are mostly shipped a lot. The character created by you would sometimes get in the "love triangle" and for some reason ruin everything. Which, is not a good thing for character creation. In this case, it's better if you make your character have a one-sided hate. Meaning, your character would dislike that particular character who is close to the person you want your character to be shipped with. You have to remember what your rival is like. If your rival is obsessed like Yuno, it should be obvious that she would absolutely hate your character when your character is shipped with Yukiteru. If your character is like Tsubaki, it's most likely that she wouldn't do anything to get in the way.