TOP 90 most common mistakes in SEO and how to fix them

In this article we've listed over 90 of the most common SEO mistakes and how to fix them. If you have any comments or suggestions about this list of SEO mistakes – write in the comments, we'll discuss and add them.

1. Broken Pages
2. 4xx Error Pages: Client Error
3. 5xx Error Pages: Server Error
4. Links with Bad URL Format
5. Duplicate Pages
6. Duplicate Text
7. Contains Lorem Ipsum
8. Duplicate Titles
9. Duplicate Descriptions
10. Duplicate H1
11. Missing or Empty Title
12. Missing or Empty Description
13. Broken Redirect
14. Redirects with Bad URL Format
15. Endless Redirect
16. Max Redirections
17. Redirect Blocked by Robots.txt
18. Non-Compliant Canonical URL
19. Canonical Chain
20. Broken Images
21. Links to Localhost
22. PageRank: Dead End
23. Missing Internal Links
24. Bad AMP HTML Format
25. Contains Flash
26. Hreflang: Missing Self-Reference
27. Hreflang: Incorrect Language Codes
28. Hreflang: Relative Links
29. Hreflang: Duplicate Language Codes
30. Hreflang: Links to Non-Compliant URLs
31. Hreflang: Missing Confirmation Links
32. Hreflang: Inconsistent Language Code in Confirmation Links
33. Long Server Response Time
34. Missing or Empty H1
35. Spelling Mistakes
36. Min Content Size
37. Images Without Alt Attributes
38. Max Image Size
39. 3xx Redirected Pages
40. Redirect Chain
41. Refresh Redirected
42. External Redirect
43. PageRank: Redirect
44. HTTPS → HTTP Redirects
45. Mixed Content
46. HTTPS → HTTP Hyperlinks
47. Multiple Titles
48. Multiple Descriptions
49. Same Title and Description
50. Query Contains Question Mark
51. URLs with UTM Parameters
52. Compliant AMP Pages
53. Blocked by Robots.txt
54. Blocked by Meta Robots
55. Blocked by X-Robots-Tag
56. GA: Non-Compliant Pages with Traffic
57. GA: Max Bounce Rate
58. GSC: Non-Compliant Pages with Impressions
59. Non-HTTPS Protocol
60. Percent-Encoded URLs
61. URLs with Wrong Hyphenation
62. URLs with Unwanted Special Characters
63. URLs with Uppercase Characters
64. Same Title and H1
65. Short Title
66. Max Title Length
67. Emojis or Special Characters in Title
68. Short Description
69. Max Description Length
70. Emojis or Special Characters in Description
71. Multiple H1
72. Max H1 Length
73. Max HTML Size
74. Max Content Size
75. Min Text/HTML Ratio
76. Canonicalized Pages
77. Identical Canonical URLs
78. Canonical URL Contains Another Host
79. Missing or Empty Robots.txt File
80. Nofollowed by Meta Robots
81. Nofollowed by X-Robots-Tag
82. PageRank: Orphan
83. PageRank: Missing Outgoing Links
84. Hyperlinks with Empty Anchor Text
85. Self-Referencing Hyperlinks
86. Max Internal Links
87. Max External Links
88. Internal Nofollow Links
89. External Nofollow Links
90. Hreflang: Missing Alternate URLs
91. Hreflang: Duplicate Alternate URLs
92. Missing Structured Data
93. Bad Base Tag Format
94. Compliant URLs with Query
95. Max URL Length
96. GA: Compliant Pages w/o Traffic
97. GSC: Compliant Pages w/o Impressions
98. GSC: Compliant Pages w/o Clicks

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• Giant indexes and Indexing Cleanup
• Breaking SEO Myths by Daniel Foley Carter
• Information Retrieval (IR) score and PageRank value