I stumbled upon this lil gem and I do recommend you to take a look and try it out!!!
One important aspect of creating is NOT to add too much. A bit of this, and a little bit of that is a very good start. Let character develop their personality and relationships through stories, not brainstorming every little detail right off the bat that'll leave no space for character development!"But I'm scared if I create a Mary Sue!"
The more you add, the more likely your character will become one. Sure a flaw here and there is good, but if they are full of them just for the fear of being a Mary Sue, you better start chopping off the most extreme ones. Not every character has to be the most tormented, most suffering psychopath in existence. The opposite is true too; not every character has to be the most holy godly saint of goody-good-doer.
Think of examples like Ironman / Tony Stark in the Marvel Cinematic Universe. He wants to do the right thing, he wants to protect his loved ones. He has the riches and intelligence to do so, but yet he suffers from depression and the fear of losing his loved ones. I look at you Pepper Potts! In the start he was this egoistic womanizer who didn't care who bought the weaponry he built!
Then comes another example; Batman. I've read many times how people say Batman is a Mary Sue. He's rich, he's intelligent, and basically has no flaws other than being a human. But that doesn't mean he's able to save every suffering human being either! And definitely not alone. Being alone was how he started, and he has gained a lot of comrades through struggles of this and that. He's not such a loner anymore. He might be still rich and have all the fancy toys, but he has gotten better at taking others into consideration. This is from the movie perspective again since I don't read the comics. My apologies.
Optimus Prime started as an iconic hero and the leader of the Autobots, who seemed to have no flaws and always won over the Decepticons. At least so was in the G1 cartoon. Occasionally the old comics depicted him as so virtuous that it backfired on the character, making him do a suicide when he lost a game due to his opponent cheating just because they had made a deal like that. Of course, being Optimus Prime, he comes back. This far, in every franchise, Optimus dies and comes back, so that's like the best character to get attached to if one fears of losing them!
Anyway, the newer the series is, the more flaws Optimus has. Just look at Animated; he's inexperienced outside of military training. In Prime he isn't able to foresee everything and in the start he wasn't thinking of human customs with the three kids until they said they couldn't stay at the base forever. And to borrow Ratchet's words; "You've grown soft", unable to actually kill his enemies unless they were meant for cannonfodder. (Poor Vehicons!) Not to mention IDW's comic continuity where Optimus is in the middle of chaos, trying his best, yet he's not able to please everyone, and not everyone wants him there in the first place.
I could list a ton more characters, but those three are just examples of how they've started; Simple and with a solid base.tldr; keep it simple at start.