Good ideas are often murdered by better ones.
Don't worry about people stealing your ideas. If your ideas are any good, you'll have to ram them down people's throats.
The best way to have a good idea is to have lots of ideas.
I have two tricks. One is that I write every day, regardless of whether I want to or not because as I just said, in a way I never want to write. It's not even an issue. I just write four pages a day when I'm working. I have a quota. A sub-set of that system is that I am a firm believer that bad ideas lead to good ones. When I am not inspired and I don't know the solution I will just type out the most banal solution and know that at least it's on the page and it gets me to the next story beat.