Two common questions I see around a lot of creative spaces - well, one question and one statement - and I figured it might be worth it to answer them both to get my own bearings on them, how they work, and just to ground myself in my own work.
Question 1: Where Do You Get Your Ideas?
You'll see this question in any thread asking a creator - be they director, actor, storyteller, writer, GM, player, whatever - about their process. In truth the answer is "my head" and a better answer is "ideas are cheap and easy, the real trick is learning to turn new ideas off so you can focus on the task at hand." Anyone who has tried writing a piece of long fiction knows that ideas just come to you. As you create your brain will just pop out ideas. Often these ideas serve to distract from what you are working on, or help your brain procrastinate from getting your word count goal for the day in.
Seriously, if you ever want new ideas for a story just google search a story prompt and start writing that. In like five pages - probably not even - you'll have a few other ideas for stories that are "so much cooler and better" than whatever you are working on.
Question 2: I have a really good idea for a story but I heard first novels never work so should I save this idea and write another story first?
No. Write the idea. Like I said above ideas are cheap it is how we execute on them that matters. Also, your first idea for a "great story" may be a great story and if it is, and you work it, it will find a home and get published. The rule is that people's first novel often just goes into a trunk, but ideas from that novel end up everywhere else. Even still, every rule has exceptions. For example, despite the rule that everyone gets rejected a dozen times before they get published my first short story I ever submitted for paid publication was accepted. I've received rejections since obviously, but that doesn't matter because the odds of that first statement being true are so astronomically low that it is ridiculous it happened. Even better is that Sabre, the story I put on submission first, got great reviews and is widely held as one of the better stories in the anthology along side big shot name brand authors like Cat Rambo and Jeff Strand.
If you have an idea for a story - a fully fleshed out idea - then you should write it. The first draft is going to suck because first drafts suck. Then you refine it and polish it with editing and if you think it is good enough put it out on submission. If it works it works. If it doesn't? Well...you still learned a whole lot from writing it and that experience will show in later works.