The following are a few of the most common issues that I see in code written by young programmers. These are also issues that experienced developers can help new developers fix by
1. Lack of knowledge of the business domain leading to an inability to understand the high-level, conceptual view of a system
2. Poorly named variables
3. Poor code organization
4. Loose cohesion in objects and functions which in part flows from bad naming
IME, these issues can be fixed on an accelerated timetable when experienced developers help mentor younger ones.
Poor database schema design. If you get this wrong it makes your life a lot more difficult and it is harder to fix. These bad models often outlive the applications themselves. You see these around years after they were made.
I deal with this every single day. The errors made in poor schema propagate through the rest of the application.
To use a metaphor: It doesn't matter how delicious of an apple you have (the data), what truck you use to transport it (the back-end code), or how nice of a store display you put up (the front-end code), if you don't store them properly along the way (the schema).
1. Lack of knowledge of the business domain leading to an inability to understand the high-level, conceptual view of a system
2. Poorly named variables
3. Poor code organization
4. Loose cohesion in objects and functions which in part flows from bad naming
IME, these issues can be fixed on an accelerated timetable when experienced developers help mentor younger ones.