- Not being willing to learn new languages and skills. Not willing to read technical books.
- Not paying attention to performance: Use of good Data Structure and Algorithms
- Not paying attention to design: Design Pattern, Object Modeling, Best Practices
- Not paying attention to security: SQL Injection
- Not paying attention to testing: Writing test cases.
- Documentation: Improper logging and comments.
- Blind copy paste making an assumption that it would work.
- Forget to take backup and remove all debugging statements like System.out.print before application goes into production.
- Jumping directly on solution. Don't start solution hunting the moment you face a problem or bug. Even if you copy from others solution, don't forget to learn and understand the solution.
- Expecting you can read intent and tone in email communication. (ASCII does not contain facial expression or intonation.) Actually reading the whole email without making any assumption.
- Not focusing on career development and networking.
- Not asking for code review and help.
- Starting with a know it all instead of a learn it all attitude.
- Paying less attention to domain, understand who the users are and why they use what we build. Understand the environment the user will be in when using your program.
- Not able to provide reasonable/reliable estimates for the task in hand. At times they become too much optimistic and give strict deadlines while other times they estimate the task much bigger than it actually is.
Source: Quora.com