All images much have an Alt Text included. If the image is purely decorative then use a blank tag i.e. alt=""
All hyperlinks should be descriptive text, or an image with a descriptive Alt Text, indicating where the link will take the reader. Hyperlinks should not be "Click here", nor should they be the raw html link.
All pages should have a H1 heading - this is generally part of each page's template.
Subsequent headings should be incremental without gaps i.e. the next level heading should be H2 not a jump to H3.
Headings should generally be written in 'Sentence case.'
Princeton's guide to accessible web content is a very good, brief guide to Authoring accessible content.
The WAVE web accessibility evaluation tool is very useful - Browser extensions are available for Chrome, Firefox and Edge to check pages instantly for issues.