Punctuation really trips me up sometimes. One issue for me is using punctuation with inverse ordering of the sentence for emphasis. Consider the following examples:
"If I were you, I would wait until next week to plan your flight."
"If you really want to go all out, I'd recommend you pick the more expensive model."
"Supposing I am your business partner, wouldn't you want me to tell you the truth?"
Note that all of the previous sentences can be reworded by taking the first phrase and putting it at the end of the sentence.
Is that comma necessary? Or is it an optional thing? This bugs me.