I need help about planning software project

Hi everyone,

I'm using C# to develop HMI softwares for our PLC projects. Sometimes it is just simple stuff show an animation, allow user to enter parameters to PLC etc. But sometimes it goes bigger, printing paperworks and reports, archiving data on database something like that.

I don't have anyone to ask personally, i am the only one in the company about software development. As i say, i don't have anyone to compare my OOP knowledge. I think i'm just an amateur. I know basic stuff about OOP, but maybe i don't know good enough. I have problem about planning my software project. I don't even know how to explain this.

I know it's silly, but i need help to improve myself. Can you tell me which subjects i should research or which books or educational contents i should check out if its ok to share in this subreddit. How do you plan your software before beginning or during the development, when to and how to use interfaces, abstract classes and other stuff about OOP? It just looked like i ask an in-depth tutorial for OOP.

Thanks everyone, have a nice day/night.