Do not spend time in the opening expanding on the queenside unless you can contain your opponent's central advances. Sunil Weeramantry & Ed Eusebi, Best Lessons Of A Chess Coach
It is vastly easier to play against someone if you always know how they feel about their position. I would say that if your body language is telegraphing your state of mind, it is costing you 50 or more rating points. James Schuyler, Your Opponent Is Overrated
In the opening the pawn-majority is not felt as a major factor, but its significance grows rapidly through the middlegame, and often becomes decisive in the endgame. Dražen Marović, Dynamic Pawn Play In Chess
A lead in development is at its most useful in open positions or in situations where the active side can achieve a central breakthrough. Luděk Pachman, Complete Chess Strategy 3: Play On The Wings
If a backward pawn sits on a half-open file, it might be weak. If it isn't on a half-open file, the pawn probably won't become a significant weakness. Jeremy Silman, The Reassess Your Chess Workbook