Comma splice

A comma splice arises when you overwork a comma, forcing it to make a stronger conceptual division than it is designed for (as if anyone really designed the comma, but never mind).

(1)

Very often, a comma splice occurs when the writer should have used a comma plus a conjunction (for, and, but, so, yet, or, nor).

Example:

My father worked hard all his life, he died poor.

The second part of this sentence is surprising, contradictory (and sad). We need a comma and a conjunction such as yet or but to alert the reader to the coming  change of pace or tone.

Thus:

My father worked hard all his life, but he died poor.
OR

My father worked hard all his life, yet he died poor.

OR, more happily:

My father worked hard all his life, so he died rich.
AND

My father worked hard all his life, and he died rich.

With the comma and the conjunction, the sentence works.

If you want to be fancy, you can eschew the comma and the conjunction and replace them both with a semicolon. The semicolon sets up the reader for the change of pace or tone

My father worked hard all his life; he died poor.

My father worked hard all his life; he died rich.

In this last sentence, however, the second part does not really catch you by surprise, in that the conclusion is the expected one - his terminal wealth being a natural consequence of working hard (if only). In this case, therefore, we might use a colon:

My father worked hard all his life: he died rich.

The colon is used to indicate something that follows on naturally from what has preceded it (dying wealthy after working hard). For this reason, it is also the punctuation we use to introduce a list, which is a natural continuation of an expression such as The xxx are as follows:

(2)

Another common error is to use the comma splice where a relative clause is needed. 

Examples: 

He has not changed his car, it is still an unroadworthy Skoda -- He has not changed his car, which is still...

He listens to music, no-one else likes it->-- He listens to music that no-one else likes.

She handed in a poor paper, it earned her an F -- She handed in a poor paper, which earned her an F.

The radio is broken, it won't turn on -- The radio, which is broken, won't turn on.