A few tips:

1.  Having a product on the market does not guarantee demand. Do your research and figure out what assets people like and what gaps in the market exist.
2. The assets I make the most money from are set as "pay what you want". If people like art, they often will donate to the artist to support them. Additionally, many people may not outright buy an asset pack from an unknown artist because they're worried about being scammed. Being able to download the pack for free means they can check the product is legit before paying for it.
3. Make as many asset packs as you can. Focus on creating a variety of different things in different styles. Track what is most popular and focus on providing more of it.
4. And most importantly, don't expect to make a living from this. If you do, you will be disappointed and frustrated. Make and sell assets for game development because you love the process and like working with game devs. This is a really fun and rewarding hobby if you stick with it, but you need to be doing it with the right mindset.