You are on lead 25% of the time and can often be the difference between a top and a bottom in duplicate.
- What suit?
- What card from the suit?
- Agressive or pasive lead?
- How does the bidding help me with the lead?
It is not straightforward.
Here are two introductory articles from MrBridges on leads
Ron Klinger's 1 hour video on leads - dated look but good content.
A good discussion on options of passive or active leads in different situations.
Standard Leads Lists
A table of standard leads against no trumps and suit contracts.
Bridgehand's list of leads.
Their videos on lead's (from 4mins point)
EBU Convention card in word (*.doc) format that include standard leads.
As always - agree with your partner lead expectations and responses.