Tips spades

Don't go for nil if you have the ace of spades. Beware the bags! It's always better to underbid than to overbid. If you have a lot of spades you might want to bid higher.

Can your partner beat a high card?

If you have the queen of one suit, there is a 55.5% chance that your partner has a card to beat it (i.e. king or an ace). So even if your hand with a queen of spades is otherwise very weak, you should not go for a nil unless you are behind by many points, as the base success rate is only 55% [you can only expect 100*0.55+(-100)*0.45=10 points from the play, and will likely saddle your partner with bags].

If you have the jack of one suit, there is a 70.3% chance that your partner has a card to beat it.

Who is undersuited?

If you have three cards of one suit, there is a 5.4% chance that someone has no cards of that suit (1.7% chance that your partner has no cards in the suit); a 23% chance that someone has only one card of that suit (8%); and 60% chance that someone only has two cards of that suit (20%).

If you have four cards of one suit, there is a 7.8% chance that someone has no cards of that suit (2.6% chance that your partner has no cards in the suit); a 34% chance that someone only has one card of that suit (11.7%); and 70% chance that someone only has two cards of that suit (23.3%).