There are a lot of definitions of SEO (spelled Search engine optimisation in the UK, Australia and New Zealand, or search engine optimization in the United States and Canada) but organic SEO in 2019 is still mostly about getting free traffic from Google, the most popular search engine in the world (and almost the only game in town in the UK in 2019):
You don’t want to “keyword stuff” and cram your core keyword and every possible variation of it into your alt attribute. In fact, if it doesn’t fit naturally into the description, don’t include your target keyword here at all. Just be sure not to skip the alt attribute, and try to give a thorough, accurate description of the image (imagine you’re describing it to someone who can’t see it – that’s what it’s there for!).
Baseline ranking assessment. You need to understand where you are now in order to accurately assess your future rankings. Keep a simple Excel sheet to start the process. Check weekly to begin. As you get more comfortable, check every 30 to 45 days. You should see improvements in website traffic, a key indicator of progress for your keywords. Some optimizers will say that rankings are dead. Yes, traffic and conversions are more important, but we use rankings as an indicator.