Self Assessment

As a writer one of the main grammatical issues I face, and utterly fail at would be the correct use of commas. I tend to put commas into every thing and to be honest I don't know when I am technically supposed to use them. I understand using the comma in basic uses like when making lists, during salutations in letters, or before using words like "and" or "but". However, I seem to use them also just to use them. I litter sentences with commas maybe to create breaks in sentences, but as my red marked essays have shown me this isn't correct. One of the situations where I am not totally comfortable in the use of the comma is when you are providing extra information about what you just spoke of. For example, in a paper I wrote about Pride and Prejudice I wrote, "After the ball Charlotte a family friend commented on this issue to Elizabeth." Upon receiving my paper back I found that I was supposed to have commas surrounding "a family friend". Although I fairly understand why it is needed here I would appreciate more information on specific reasons why it is needed here. I would hope to learn the correct usage of commas so that I can gain the confidence to use them. As of right now I am beginning to just completely phase out the use of commas. I would love to find the happy and correct medium of comma usage.
Another grammatical issue I have is something that is totally unknown to me, the semi-colon. My high school English teacher told my class not to worry about using them and that we didn't need to have this knowledge for her class. Unfortunately, I would like to have this skill so that I can apply it in my writing. I would love to be able to provide an example of where I am confused about the use of the semi-colon, but I know nothing about it, a blank slate if you will. Basically, I am going to need an entire lesson on the semi-colon at the moment I am terrified of it because it is a stranger.
The final issue that haunts much of my writing is switching between tenses. I understand that when writing you need to pick one tense and stick with it, however as I write I switch back and forth frequently. I believe that I need to work on the skill of proofing my paper to correct this. I was hoping that there would be a tip or idea that could help me identify when Ia m switching back and forth as I don't always pick up on it as I am reading. Most of the time I seem to begin in past tense and then float back and forth between it and future tense which confuses the reader and makes my writing look weak.
Overall, these are the three issues that I feel weaken my writing the most. The improper use of commas, the vacancy of the knowledge of the semi-colon, and the inability to use one tense throughout an entire work.