HTML tag with SEO

Bold 

1. Important text / keyword = Use <strong>...</strong> tag
2. Normal text = Use <b>...</b> tag

Italic

1. Important text / keyword = Use <em>...</em> tag
2. Normal text = Use <i>...</i> tag

Underline

1. Important text / keyword = Use <ins>...</ins> tag
2. Normal text = Use <u>...</u> tag

Inside Head Tag

1. Search result shows the title of the web site. <title>Very Important</title>.
2. <meta charset="UTF-8"> UTF-8 support all language.
3. <meta name="viewport" content="width=device-width, initial-scale=1">. This line show 100% for any device when load.