When it comes to reality checks, you’re trying to build it in to be a habit and a process that you do constantly. The main thing that will help to work on isn’t just the action of the RC. If you get an action down that’s fine, but it won’t be enough. I’ve had RC’s show I was dreaming before and I just rationalized it away. You need to make sure you have a good thought process behind it. You need to make sure you’re actually questioning whether you’re awake and dreaming. Just remember, you might feel sure you’re awake, but you feel that way when you’re dreaming too, right? Maybe you should RC just to be safe…
In terms of how often… it’s more of a constant process. Here’s an article I’d really suggest you read.
https://community.ld4all.com/t/the-secret-of-frequent-lucid-dreamers/33764
And for my shameless plug, here’s an article I wrote that also kind of touches on this subject.
https://community.ld4all.com/t/the-importance-of-awareness/36662