Okay.. let's go.
Get inspiration, seriously. You can't just sit behind your computer for hours and think: "I want a badass new OC that will own everyone!" Get your inspiration from your hobbies, or real life examples so you will continue to enjoy RPing your OC and not just put them on hold after a month.
Example: My Shinigami, Tōga Hiro was created while I was playing FC4. I was like damn that Pagan Min guy would make such an awesome character. That was my inspiration.
Flesh out your idea. Get your ass on Google Drive, create a document and start thinking of combat abilities in the world of Bleach that would fit with your character. Since Pagan Min lives in Kyrat, which is close to where the buddhists live who live with tigers and stuff I don't even know, I was like: I should make his Zan something that has to do with wind materializing into tigers and shit. Think of a backstory, how and why would they become a Shinigami? Where did they start? How do they act? You can think of a entirely new personality but you can also base it off your inspirations. Pagan Min is this psycho dude that has no problem killing your entire family so my OC is really batshit crazy.
Make a few posts with your character in your Google Drive, so you can get the hang of how they would act in interaction with other people. Will other RPers likely ignore your character because he's so rude and wants to fight all the time? Edit his personality so people will find him interesting and want to learn about your character.
Get yo shizzle approved by mods and balance him/her accordingly.
RP your character, expand his story. Develop your OC through threads and interactions with other characters. Make connections, bonds and after about 6 months, your OC will start to look complete. Your OC is NEVER EVER finished, keep developing them.