Technical SEO
Is the site mobile-friendly?
Does the site load in under 3 seconds?
Are there any 404 errors or broken links?
Is there a valid SSL certificate?
On-Page SEO
Does every page have a unique Title Tag?
Are Meta Descriptions compelling and under 160 characters?
Are H1, H2, H3 tags used correctly for hierarchy?
Do images have descriptive ALT text?