Semicolon use
A semicolon following an independent clause [a complete sentence] signals that what follows is also an independent clause whose meaning is of equal importance to the first. Joining two clauses with a semicolon alone is appropriate only when the clauses are closely related and the relationship is clear. If they are not closely related, you probably should make them separate sentences. RULE: Although an independent clause following a semicolon is essentially a complete sentence, it never begins with a capital letter. Unlike a coordinating conjunction [and, but, for, or, nor, so, yet), a conjunctive adverb [however, nevertheless, accordingly, besides, indeed, similarly, then, thus, therefore, that is and others, or a transitional expression ["in fact" or "for example"] cannot be used with a comma to join two independent clauses. Conjunctive adverbs and transitional expressions require a stronger mark of punctuation: a semicolon [I wasn't busy;however, I did not have time to play golf.] 2) "When items in a series contain commas, readers may have difficulty deciding which commas separate parts of the series and which belong within the items. To avoid confusion, put semicolons between elements in a series when one or more contain other punctuation.[Confusing: "I interviewed Debbie Rios, the attorney, Rhonda Marron, the accountant, and the financial director." Edited: "I interviewed Debbie Rios, the attorney; Rhonda Marron, the accountant; and the financial director."] (The Longman Writer's Companion).

source: http://www.drgrammar.org/faqs/#14

Hi,

Here's a general and subjective comment about semi-colons and colons.

The first time I taught these to my class, I found that everyone's writing became full of them. They appeared in just about every sentence.

Now I tell people that one semi-colon and one colon per essay is enough, and maybe even too much.

Best wishes, Clive

Hi,

Can I put 2 commas in one sentence? e.g: Firstly, If you've done your job, you'll go.

Yes, more than one comma is OK.  ( In your example, don't capitalize 'if'. )

Best wishes, Clive