1) don't make them a Mary Sue. It's never good to have an oc who is perfect, everyone is attracted to and is mga kaibigan with everyone. Giving thm some character flaws will make them madami relatable and well rounded.
2) Make sure to watch your grammar and spelling. This has less to do wih the actual character of your oc and madami to do with the presentation. The madami clear your bista sa tagiliran is, the eqsier it is for other people to understand and the easier it is to portray them correctly.
3) Go into detail. If you want yor oc to seem like a real person it is important that you decribe every aspect of their personalities, their fears, their dreams, what really makes them angry and so on.
4) A decent background history. Try to describe their past, family, friends, upbringing and important events in their lives as best as you can. Just make sure to make your character live sa pamamagitan ng events that happened to them. If your oc was abuse or betrayed sa pamamagitan ng someone for example, they may not be he most trusting person.
5) Try not to make them a rip off of a character from the fandom you've made them for. It's not interesting if your character has has just gotten out of juvie and spends his/her time picking on Harold.