If you read the pessukim or words out of order you aren’t yotzay. However, if you read the parshios out of order it’s okay. (ShA 1)
If you mistakenly skipped a certain possuk, you must return to the beginning of that possuk and continue in order. (ShA 2)
If you skipped a word, return to the beginning of the possuk that the word is in – then continue in order. (MB 5)
If your mind wandered and then you found yourself at a certain word in the middle of a paragraph, you can safely assume that you didn’t skip any pessukim or words. (MB 10)