I second Michael's recommendation to check your safelight. Please consider using the Kodak test, and not a "coin test" or its variants. It will only take 10 minutes.
Unsafe safelight that does not fog paper will reduce contrast and it will force you to use excessively hard contrast filtration, in addition to causing other issues with print-to-print consistency. Second to that would be checking your enlarger for significant light leaks.
I would say that 4 our 5 darkrooms which I have visited had unsafe safelights. All the other suggestions, which you got, are pretty good too.
If you don't have a densitometer, what's wrong with the coin test?