Visual marketing ideas and concepts - How do I present myself to the marketing world?

Hi Everyone nice to meet you all and be involved in this community. I am Sam, I have been working for myself in retail and event design for 20 years, designing graphics and visual concepts. I have always as long as I remember been interested in making images and visual ideas for marketing and spend endless time looking at campaigns and Ads thinking things are not as good as they could be and opportunities and messaging are missing. I have made graphics for many large brands in the retail and events space and whenever I have got involved in any concept design it goes really well but most of the work the concept has already been established and I am following on with that style. I had for example a job visualizing an event for the launch of a new Sony phone and the events agency asked if I could make up some extra background graphics to show off 5 key features of the phone, Sony loved the graphic ideas I made and asked if they could use them in their main campaign imagery, I have had this happen also with other brands so I know the energy I have about marketing graphics is where I should be. My question is how do I approach the world of marketing to get myself seen so I can do more of this, how would I describe myself and who would I talk to. When I read up about marketing on google I grey over with all the detailing finding it hard to see how I can get involved without having some kind of comprehensive marketing spiel but I am overflowing with visual creative ideas and want to get involved in the marketing field. The ideas I get are my own concepts most of the time.. I have a big idea in my head for a campaign for weetabix cereal for example and would love to draw it up and send it over to them, but how would I pitch it to them in a way that is professional and in a way they would see it as a serious creative idea for example? .... Thanks if anyone can help !

Sam