Looks around, this is my first post as well.

My biggest Grammer problem is ... US spell checkers, or spelling. Drives me nuts.

Colour - has a u in it. Any time I have web page issues first thing I check is how I have spelled colour.

As a really bad speller, it is the one thing that can kill a story for me. I read so fast that a paragraph down, my brain goes what the! Leshes or something was the last one.

Weirdly, I was always taught that a comma is used around a part of a sentence that means the sentence can be read without it. I do use it before and, but it is a question of flow for but. A long time ago, in the same place, I was taught that a full stop is three seconds, and a comma is one so when you read your work, try that. I find it often calls for massive rewrites.