Keyword stuffing is one of the common mistake in SEO. In order to get high rank in search engine they stuffing keywords or phrases in the paragraph to make the web pages to the top of the ranking. At first it will get to better rank but later google understand keyword stuffing and it will low rank the page then you cannot able to get high rank. If your keyword repeated over and over again on the webpages then the visitors are hesitate to see your page and they left your website. It will cause so much of bounce for your site. If there is so much of bounce in your site then you will not able to get high at any time.
Duplicate content refers to content of the webpage is identical to content of other web page. Duplicate content causes google hard to show to show webpages Which webpage is relevant to keyword. Your should be unique when compare to other content then only your will able to get high rank. Duplicate content causes discourage to visitors and they will not visit your site afterwards.
Broken links or Dead links are the links that doesn't exist on the webpages. This is caused by the url which we entered in our website which was removed by the web owner it leads to 404 error. Broken links also caused due to entering incorrect links of the url and also by improper url entered by the website owner. Broken links also formed when the user has a firewall that blocks the destination website. When broken links clicked by the visitor an error message will form on the display as not found. It will low rank your page.
No unique title tag and meta description
I have seen in many websites that title tags are same. Identical title tags not make your website to high rank. Your title tag and meta description should be unique and it related to content on your webpages. Then only your visitors can able to easily understand your website. your title tag and meta description should not differ from content and also the title tag should not copy of the other webpages. Your meta description should be within 160 characters so that the description can be viewed by the visitors. Meta description and title should tell the entire content of your page and also it should be unique.