Just as in any other season or year, you should be selling stuff that people are going to want to buy in the future, not what was popular in the past. So if you're selling stuff on your Etsy Shop that did well 4 years ago, it probably isn't that popular today in 2018.
That's often times why New Etsy Sellers do better than Old Etsy Shops that have been on Etsy for several years. New Etsy Sellers think about new problems to solve, while older Etsy Sellers get stuck selling the same thing over and over and seeing their sales constantly drop.
So when you are making new products on Etsy, consider these 3 principles:
1 Create designs you enjoy making
If you don't enjoy making it, and you're not passionate about the topic, your Etsy Shop will be a huge burden to your life. Make what you love doing, but also what other people are going to love as well.
2 Think about what's going to be popular in the future, not what was popular in the past
Again, Etsy Sellers have this tendency to stay stuck selling what they used to sell over and over. Instead, think about how you can solve upcoming problems in June, July & August of 2018, instead of re-selling solutions that worked in the past. This means you will be constantly experimenting with new ideas and product designs, but that means more opportunity for more customers and more sales.
3 Think about how you will solve your customers' problems
If you're just trying to sell stuff that you think people will buy, without solving a specific problem or helping people attain a particular mission or goal, you might get sales in Etsy, but not that much. Don't just do what everyone else is doing. Think about how your products or services can truly help other people solve their problems. It could be a matter of aesthetic, price, materials, quality, or something very useful or helpful. Whatever problems you are trying to solve for your customer, that should drive your product design, instead of just trying to sell things that other people seem to be making.
Your Etsy Shop should be constantly growing & changing. Think of businesses that have gone out of business recently. Toys R' Us has barely changed their business model in 20 years, and went bankrupt. They didn't want to change their business model, they just relied on techniques that worked in the past and saw sales drop year after year. That's the same reason why Etsy Sellers see their sales drop. They keep doing the same thing over and over and expect Sales to just roll in like they used to.