@silver1the1hedgehog some tips I can give is;
1: Make your protagonist believable and realistic.
2: OP characters are usually not a good idea as readers enjoy reading conflict and struggle.
3: If you want to do an OP character the antagonist has to be either just as strong or be superior in another sense. A good example is your protagonist could be stronger, but your antagonist is smarter.
4: Plan out characters as much as possible that way you can reliability come up with how they would react or solve situations.
5: A good little exercise I like to do is take whatever character I am making and putting them in different situations and think how they would respond, they don't even have to be situations revolving the actual story. Helps build who they are and what their ideals are.