You need to do alot of research daily. SEO is constantly changing and keeping up to date is crucial. You do not need to pay someone money to do it either. It is just knowing what you are doing. good luck.
it may look better if you increase the font size of the subcategories
list all the subcategories under each category.
now there are only 3 sub categories listed on the main page.
if there are many subcategories, then list the important ones among them on the main page.