Today’s English is much less formal than when I was an English Lit. major at San Jose State University! Commas and semicolons are hardly used, except for obvioius adverbial clauses like, “When I was in college, I wrote with more commas.”
By-and-large reading your writing out loud really helps you determine where a period, colon, seimi-colon, or comma goes. The “breath-breaks” or pauses you need when speaking or reading your essay, usually requires at least a comma ( , ). When you are introducing an example or a list with statements “like the following,” or “for example” — use a colon (:). In the middle of that list you are giving (after a colon), a semi-colon is required.
Finally I like this useful test when writing and using adverbial clauses, you know, the phrases beginning with words like: when; while; where, as, since, if, although, or because. If you can ‘bend and flip’ the sentence around and it still makes sense, then you need a comma (,) right there. For example:
Since I’m done with what I want to say now, I will say goodbye… OR
I will say goodbye, since I’m done with what I want to say now.