How can I know my SEO is improved?

What is your SEO Target?

Before you start your SEO work, you should define what your SEO target is. You should set a SMART goal that stands for Specific, Measurable, Achievable, Relevant, and Time-based. In the beginning, I suggest you set 5 - 10 target keywords to rank high.

Define your keywords before everything

So you would ask what is a suitable keyword, right? A good keyword is a keyword with a sizable amount of search volume and a medium CPC (cost per click), say 5,000 - 10,000 / month search volume, and $5 - $10 CPC on google ads. If the keyword is too competitive, it will be very hard and takes a long time to appear on the first page.

Always remember that you're NOT an SEO expert, it's not necessary for you to master all areas in SEO. On the contrary, you should focus the niche keywords which can generate organic traffic for your store. If you can take a slice from the keywords advertisers are bidding, you are saving your budget on ads.

Also, create backlinks with the niche keywords can help you to generate traffics from external sites and build backlinks.

Track keyword performance

I would suggest you using the common tools:

Google Analytics

Just install GA on your store. If the traffic is growing steadily, you are on the right track. Since GA is too common nowadays, I will save my words here.

Google Search Console

Besides GA, Google Search Console is another must-have tool for SEO. In short, you can

Submit your sitemap (sample sitemap.xml file) to Google. Ask Google to regularly indexes your store
Check how many impressions and clicks are generated from Google Search
See what queries are generating the clicks and impressions
See what pages are causing errors. These pages are very likely dead links

Ask the customers

Finally, ask the customers where they discover your site. It's probably the simplest way. Ask the customers you have answered their questions.

3rd party keywording tracking tools

You can use a 3rd party tool to track the search positions against certain keywords.

Finally, Iterate!

After tracking the keywords, you should occasionally optimize your SEO work to maintain the search position. For online stores, the most effective way is to create blog posts, Youtube videos, or other valuable content. Unique content is a lead magnet to drive traffics from Google.