Commas are a killer. At certain course levels, I would say that an unbelievable 15% of errors relating to grammar stem from commas (,). The best advice that I can provide students on this topic is to reduce the number of commas that you need to use in sentences by making short sentences. Naturally, this produces a greater number of short sentences.

Following this advice will result in texts that are less artistic and less pleasing to read; however, since these are English as a second language courses, a lot of emphasis is placed on grammar. A typical evaluation places 40% of the grade on grammar and only 2% on "style." Which one would you rather lose out on?

In short, avoid crafting sentences that require commas unless you are absolutely required to use them. A table, below, distinguishes between unavoidable sentences where you must use commas (left-hand side) and sentences that you should not write in order to avoid using a comma (right-hand side):