You want to write games? Gaming stuff? Scenarios? Army lists?
Cool. You can.
You can literally sit down right now and do it.
It's like anything else in life: Maybe you'll have a knack for it and it just comes naturally. Maybe it turns out you don't quite have the mindset and you gotta work harder.
Ultimately, it's usually a question of hours put in. Work more at it, the results will improve.
Try to do new things. Challenge yourself. Do things you're told are impossible.
Here's the thing though:
Along the way, you may find all manner of short-cuts to success (here defined as "making some sales).
They're appealing exactly because they're easy.
You can hitch yourself to a marketing fad.
"Old school dungeon crawling fantasy RPG" will earn you 50 sales even if you have literally nothing new to say on the topic.
Solo miniatures gaming seems to be blowing up right now and there's room for plenty more there.
Just make sure you're on the train when it's going up hill, not when it's coming back down.
You can tie yourself to a brand or product identity.
Plenty of companies have options out there to make stuff with their name on it.
If what you burn for is [system X] then that's an easy path.
They'll ultimately control your fate of course. What's the thing Darth Vader said about deals changing?
You can cash in on internet culture wars.
Find something that you know will make someone somewhere mad. Write that.
Wait for someone to write a blog post saying your game is garbage.
Rally the people who dislike that person and you can roll in protest-purchases.
"Pay me 9.99 to fight SJW's" is a deal you can easily make a car payment or two on.
* * * * *
Ultimately though there's another solution:
Write stuff you actually care about and feel strongly about.
I strongly believe that good design and passion will always be recognizable.
More importantly, it'll give you an identity as a creator that people can connect to.
More importantly while you may get a few less sales, you'll be getting sales from people who are interested in what you have to say.
And that's why you're here right?
Because you have something to say about gaming?