That's good advice. Another thing I've found is that when it looks like the clues are insufficient, what helps to solve is looking harder at the "later / earlier" or "more / less" clues.
Also, when I've gotten stuck many times what helps is looking at the "five people are" clues. Each of the 5 should take up one row of the grid. Look across the rows that are missing a circle and see if one of the 5 will fit there.
Each puzzle actually has enough clues for solving if you can recognize them. Hope this helps.