The use of linefeeds (CTRL-J) as the first and last character in the text of your REMs (see example below) makes the text of the remark stand out. Some printers even place the remark at the left margin with the line numbers.
Using colons to indent FOR-NEXT loops makes them stand out, making it easier to identify those needing closing.
10 REM THIS STANDS OUT
20 FOR J = 1 TO 10
30 : FOR K = 1 TO 10
40 :: PRINT J * K
50 : NEXT K
60 NEXT J