Easy. First you survey the existing literature for your theory. Chances are, somebody already came up with it, or, more likely, debunked it. If that's not the case, you write up a paper, presenting your theory together with its supporting evidence and submit it through the usual channels. I know that sounds pretty discouraging, but the chance of some rando contributing something meaningful are pretty close to zero

Oh you're a programmer? I have this app idea...

Write letters to the press. Ripped from Control:

Dear New York Tribune,

Airplanes aren't real. I figured out how they do it.

The windows are TV screens. The whole thing moves on big tracks like a rollercoaster that moves through underground tunnels in the Earth. Airports are more like train stations.

They do this because the sky is full of monsters that they don't want us to know about. The planes we see in the sky are the monsters. The government made the Earth-trains look like the monsters so they could lie to us better.

Don't contact me.

Not real, obviously, but clearly the most effective tactic when no one takes your 100% legit theories seriously.

First of all, if you have a theory they rejected, clearly its because they are afraid of your massive intellect, pure jealousy to the point of refusing you entirely. So that means your theory is 100% fact, and you should write a book all about how you are a genius ahead of their time, and sell it on Amazon becoming a number 1 best seller and use that to propel you into micro-celebrity status and live off the royalties because thats what smart people do. Duh.

There are 99 crackpots for every genius without a degree.

"I have theories" is great, everyone should have theories and ideas.

But if you can't connect them to understood, known physics and systems that have been demonstrated over and over again for centuries, you're not really contributing anything.

"I have ideas for a really cool race car shape. I don't know anything about formula 1, I just have this neat idea. Why won't professional teams who demonstrate their efforts daily take my design seriously?"

Go to school, educate yourself with online courses, read every possible criticism or attack on theory, be your own worst critic and THEN if it survives knowledge and critique, you have a chance of being seen and noticed. This isn't about "encouragement" or "making someone feel better" and it's certainly not a plot by Big Science to keep the little man down, this is just how the process works and why you have phones and video games and soda dispensers.

It reminds me of this...

My brother in law was telling me about this amazing new tech called a Thunderstorm Generator which apparently filters out carbon from combustion engines. After seeing this... I just can't... It's too much...

Hi. People contact me with theories all the time based on my published research. They tend to come from an oversimplified view of the problem.

It's a special kind of stupid to be too stupid to understand that you're stupid, to be so stupid you think you're smart. Man, what a life that must be, blissful ignorance.

The maths department in my uni receives (or did when I was there) several proofs every year on general formulas to solve equations of degree >5.

physics crackpots: a 'theory' - Angela Collier

The biggest problem is that your theories are not going to equate to the depth, degree, and experience of people who've been over a decade in Universities studying their own, who receive grants and everything to do so. It may be a revolutionary theory, but every scientist has got their own. That's what you are competing against. Hell, there are plenty of brainiacs at each other's throats over whose theory they believe is right.

I have a personal theory that I believe can encompass a lot of phenomenon, but I lack the graduate level experience or the extraordinary intelligence to raise eyebrows, so it has to remain largely faith based. There are much more knowledgeable people who dismiss the basic core tenets of it. And unless you map it out onto some real math and start making predictions that can raise eyebrows, it will remain that, faith-based. Society doesn't give a shit about ideas, they give a shit about implementations of those ideas.

The theory? 1x1=2

ITT: Science and Engineering users debunking others attempts to contribute from an entry level

And then there's Maths where all you need is a fresh pair of eyes.