Parallel fifths/octaves
Parallel fifths and octaves are pretty basic musical errors. They aren't that difficult to understand, but they can be pretty tedious to find.
1. (Optional) The first thing I usually do is LABEL EVERY PITCH on the paper (As A,B,C,D,etc.) This method may not appeal to everyone because it is a bit taxing, but it is a way to be very accurate and makes finding fifths especially easier to find.
2. LOOK FOR PARALLEL MOTION. Don't waste your time trying to analyze every single chord on the page. Look for the pitches that move together, it should at least be obvious whether or not they are moving in opposite directions.
3. If you find a chord that meets these qualifications, check for FIFTHS AND OCTAVES IN A ROW. For there to be a parallel fifth or octave, it can't just be a fifth, you have to be sure there are two fifths (or octaves) in a row and they have to move by the same amount.
2. LOOK FOR PARALLEL MOTION. Don't waste your time trying to analyze every single chord on the page. Look for the pitches that move together, it should at least be obvious whether or not they are moving in opposite directions.
3. If you find a chord that meets these qualifications, check for FIFTHS AND OCTAVES IN A ROW. For there to be a parallel fifth or octave, it can't just be a fifth, you have to be sure there are two fifths (or octaves) in a row and they have to move by the same amount.