A lot of newer players mistakenly think leads are luck-based. It's true that on a single hand there's a lot of luck involved. But in the long run, an expert player gets a very big edge from good leads. Opening leads are all about:
Is there a need to take risks and lead aggressively? If not, what are your best passive leads?
Is a trump lead indicated?
What is our goal for the hand — are we trying to force declarer?
Leads during the hand are often about:
What holding does dummy have? Lead through strength and towards weakness.
What are my goals for the hand — setting up partner's suit?
Is there a need for me to open up the suit, or can I play passively?