The best part is about setting this sort of goal is that these 500 words don’t even have to necessarily be good. Obviously, if you can write 500 words about a topic you feel passionately about and is worthy of being published, then you should absolutely do so. But there are days, like the very day I’m writing this, that I simply don’t exactly know what I should write. Every writer has days like this. It’s only human to have days in which you simply don’t want to work. But it’s important to have this absolute minimum of 500 words, because if you don’t, you’ll find that there are days where you simply write nothing at all. Then when you try to start again, it can be a struggle. Maybe this isn't true for everyone, but I've found that I have to continuously exercise those writing muscles, they can ache pretty badly once I try to start again.
The best thing to do when you’re really stuck for a writing topic is just to write about whatever comes to mind. It doesn’t have to make sense or even be anything particularly interesting. It doesn’t have to be anything you will end up necessarily publishing anywhere. The simple act of making words come together is enough to keep those writing muscles from atrophying. You don’t have to go back and proofread or even spell and grammar check what you wrote necessarily. Something just has to come out on the page in front of you, whether it’s on paper, a computer screen, a tablet or whatever. Actually, sometimes if you typically write on the computer, try just grabbing a sheet of paper and scribbling down whatever may come to mind. Likewise, if you often work in paper notebooks, try typing something up on your computer or similar device. Heck, even write something on your phone’s memo pad if you have to. Whatever little change of scenery will help, you should make simply to get some words out.
If you’re working on a book project, then you should aim higher than a 500 word minimum. However, it is a good minimum to set for yourself. Five hundred words a day is 15,000 in a month. In three months, you’ll have written the equivalent of a short novel (45,000 plus words). Maybe not all of it will be good, and some of what you write may be nothing but the outline for ideas of what to later write about. But it’s progress. Some days you’ll just write more, and if you feel you must set higher minimum word goals for yourself, then by all means do so. Just write at least 500 words a day, and guaranteed, you’ll always find yourself with something to work from!
(Note: This article alone is about 600 words)