Is ritual necessary for a successful outcome to a spell? I mean do I have to follow a traditional ritual or can I develop my own?

You can use your finger instead of a wand, if you want. Ritual is to help with concentration, belief in the outcome, and intent. You can always develop your own, but as with any craft, there are basics that should be learned before you make up your own. For example, my best friend is an incredible guitar player. He plays lead and makes up his own rifts all the time, but he had to learn the basics of guitar playing first. It’s the same with magic, cooking, pottery, anything.