Head to google trends on your computer.
Start with the first topics on your list and put one at a time into the search bar.
(SEE IMAGE BELOW)
You are looking to see how the topic trends and if it is profitable.
I used gardening and beauty treatments as the 2 examples.
As you can see gardening is seasonal and would not be a good niche unless you only want to make money in the summer months.
Beauty trends is a good one but too broad so google made some suggestions.
When you type your topic into the search bar you will see suggestions. Some of these may be a narrow down of what you are searching.
At the bottom you will see suggestions also that you can search to narrow down you niche.
You may want to search some of these suggestions to see if the trend is better.