Density: I make this mistake often. I end up chaining multiple thoughts rather than splitting them up into discrete sentences that link thoughts together. It maybe easier to write but it's harder to read.

I use commas for things that can be mentally skipped and lists, and semicolons for related sentence fragments. It's probably an anti-pattern to use semicolons except as a greater grouping like: do you want apples, pears, and bananas; chicken, fish, and beef; or lettuce, tomatoes, and onions?