Opening Leads for newer players: Lead Your Longest Suit in No-Trump
When defenders face a no-trump contract, one default rule is extremely useful:
Our goals are often simple, but its worth actually spelling them out.
Try not to do harm with your lead - try not to give opponents tricks they are not entitled to.
Try to do good with your lead - try to set up tricks for your side.
Your longest suit is often the suit your side will want to play in order to set up tricks. Also, with longer suits you are often less likely to give tricks away or destroy a trick you might otherwise have been entitled to, if you had not touched the suit altogether.
The core idea
Simple examples
If your suits are:
Spades: K9752
Hearts: 84
Diamonds: Q73
Clubs: J96
A spade lead is usually your practical beginner choice, because spades are your longest suit.