Depend of your taste, trichomes is used to know the best moment regarding THC and other cannabinoids, but you can use your noze every day by putting your fingers on the bud and smell accurately. (hand washed for sure ! )
Also you can use the senescence, some people wait for the fan leaves gone yellow and plant practically die..
Last you listen to your reason, by learning the plant himself, like a person you want to say "I love you" but you need to wait the best moment to do it, listen to your heart 😌