If you are starting an independent clause (a group of words containing a subject, verb and expressing a complete thought) with the word so, you have two options:
1. If the clause in front is short and easily fits with the new thought, then place a comma before so.
The photocopier is constantly breaking down, so we will buy a new one this month.
2. If the preceding clause is lengthy and you need a break in the thought process, then place a semicolon or period before the so.
Despite repeated attempts to remove the mould from the building, we are still not confident that we have completely fixed the problem. So I would like you to consider relocating your office.
Remember so as a conjunction means therefore. So that means in order that.
The RFP must be completed on time, so you will have to work overtime.
The RFP must be completed on time. Therefore, you will have to work overtime.
You will have to work overtime so that the RFP is completed on time. You will have to work overtime in order that the RFP is completed on time.