most important factor in an SEO campaign:
Keyword density
meta title, meta description,
content
responsive site
fast page loading speed
headings tags etc
There are three elements of successful SEO campaign:-
1) Keyword Research
2) On Page Optimization
3) Quality of Content
In ON Page optimization there are various element, but some of them need to be optimized perfectly, like Page Title, Description, Internal linking, Alt tag.
Every aspect of SEO whether it is on onpage or offpage it is important. Though keep in mind that when doing SEO for the site don't just focus on search engine alone but make your target audience also your top priority. And I think that is the key to be successful in SEO.
1. A Well Targeted Keyword Focus
2. Strong Page Element Optimization
1. Page Headings
2. Page Title
3. Image Alternate Text
4. Link Anchor Text
3. Good Quality Page Content