What are the possible errors that make a link bad for SEO?

Dont use low quality content and low quality sites. Always use strong content and attractive content. Content should be written with relevant information. Dont get link from irrelevant sites. Content should not be over promotional.

I think that don't use low backlink website where you are getting backlinks.

Don't use keyword again and again on every place.

Chek your webmaster tool that Google is indexing or not.

Using spammy and duplicate content for submission and irrelevant subimission on sites not related to your niche.

1. Sites using for links bulding should have DA greatert then 35
2. Spamming work should be avoided
3. Site content should be content word count
4. Content subbimated in irrelavent site  

Common URL Related SEO Mistakes:

Website owners and agencies alike, please refer to my “Common URL Related SEO Mistakes” cheat sheet and maximize both your search engine visibility and usability in one go!

1.   Lack Of Keywords

2.   Too Many Keywords

3.   Semantics and Directory Structure

4.   Dynamic AJAX Content

5.   Canonicalise www and Non-www

6.   Secure HTTPs Pages

7.   Category IDs

8.   Session IDs

9.   The Trailing Slash Conundrum

.   Index File Rendering

.   Subdomain URLs

From an SEO point of view don't use low-quality website to make backlinks, put rich content so that user are more engaged.

1. Many keywords
2. Irrelevant data

One of the most common errors that occurs with outbound links (links to other sites) is the 404 (page not found) error indicating a broken link. Since you can't always control how other sites perform, it is up to you to make sure that a link works before adding it to your page and perform regular audits to see if the link needs to be changed to another relevant source.

When adding outbound links always make sure you are following best practices such as:

• Using natural link anchor text and avoid using keyword phrases because they come off as spammy and make your intentions cheaply obvious.
• Use relevant and authoritative websites as sources
• Avoid linking to spammy websites that use alot of ads and pop ups 
• Always check if the link your adding is working or not

Dont use low quality content and low quality sites. Always use strong content and attractive content. Use link building tools to check your competitor linking and create linking accordingly.

Don't use duplicate conent . TO create do-follow link. Do not create link irrelevant sites.

A link with a high spam score, or a PBN network blog which is a grey-hat kind of links, a low DA website.