Many of these are guidelines and not set-in-stone rules. There will always be some exceptions!
Never count distribution and high card points in the same suit, unless it's an Ace or AK combination.
If your partner is bidding in no trump, don't count your distribution points in deciding on a bid.
Never open a major suit unless you have five of them. This is especially true if you are the first or second seat.
Length over strength: Open bidding with your longest suit, even if another suit is stronger. With two equally long suits, open the higher ranking suit.
The response of a game contract to a pre-emptive bid is a signoff bid (meaning, the bidder does not intend for you to respond with a higher bid). Generally the best response to a pre-emptive bid is to support the opener's bid.
A 2 trick failure in your contract is better than opponents' success in a game contract.
Bergen's Rule of Twenty (used when you are unsure whether to open in the first or second seat): add your HCP, not your distribution points, to the number of cards in your two longest suits. If you have 20 or more, you can open at the one level.
The Law of Total Tricks: the total number of tricks you can take tends to equal the total number of cards in the trump suit of your best fit. A partnership tends to be safe if they bid to a level equal to the number of cards in their trump suit -- with a 9-card fit, bid to the 3-level.
Second hand plays low, third hand plays high.
In all finesses, the lead must come from the hand opposite the critical holding.
It is usually correct strategy to develop winners as soon as possible. Sure winners like Aces and Kings can wait and may be useful for regaining the lead.
Always cover an honor with an honor.
Play a high card from the short hand first, to avoid transportation problems later.
In a solid suit missing the Queen, 8 ever, 9 never. (finesse with 8 cards, play for the drop with 9).
In notrump, declarer focuses on establishing extra winners. In a trump contract, declarer focuses on eliminating losers.
In notrump, get your losers out early to keep control at the end.
An even number of cards are probably divided unevenly, an odd number of cards are probably divided as evenly as possible.
Don't use an Ace as an opening lead unless you also hold the King in that suit.
A side suit singleton is an attractive lead when there is a trump suit.
Defenders should lead trumps early and often when a crossruff is looming.
Against notrump contracts, lead your fourth highest card from your longest suit. Don't forget the Rule of Eleven: assuming the 4th from the top was led in a NT contract, subtract that card from eleven, and you will know how many higher cards are in other three hands.