1.

Hand evaluation -

Honor strength - While HCP evaluation is:
Ace = 4, King = 3, Queen = 2, Jack = 1
in reality, Aces are worth nearer 4.5 and Jacks are about 3/4

Primary honors (Aces and Kings) are more valuable than secondary honors (Queens and Jacks)

Intermediate body cards (10, 9, 8) may offer extra tricks in longer suits

Suit concentration, such as two-suited hands, often provide opportunities to take additional tricks

Honor concentration, honors in same suit and particularly suit sequences, also provide trick-taking opportunities

Working honors in partner's suit are valuable

Shortages, especially the opportunity to cross-ruff side suits, offer opportunities to take extra tricks.  See Distribution Count Methods, Short Suit Points, and Losing Trick Count

2.

Vulnerability - affecting both game/slam bonus premium score as well as consideration to make a sacrifice bid

3.

Initial seat - many competitive players open with fewer points in third seat than first seat.  Also, from a tactical perspective, preemptive bids are best in third seat and least productive in second seat.  In the second seat, the player has a 50 percent likelihood to preempt partner, versus no chance to preempt partner is third seat.  Also see Bridge Notation

4.

Relative seat - when a player is holding tenaces (honors) "over" Right Hand Opponent's bid suit, finesses are more likely to win tricks.  Also, in passout/Balancing Seat, players often stretch to compete by keeping the auction alive, as opposed to partner's bid in the direct seat shows extra values.

5.

Passed hand - when a player is a passed hand, the possibility of making game or slam is less certain.   In this situation, responder's new suit is not a forcing bid.

6.

Psychological aspects - various emotional considerations affect a player's bidding and play, including: cumulative score, partnership trust, discipline and reliability, "mastermind bidding" (making a unilateral call), concentration, emotional compatibility, memory (short and long term), "stock market" mentality (fear and greed), "catch-up" syndrome (trying to retaliate or recover after a bad hand, risk taking/adversity.  See books on Psychology of Bridge

7.

Knowledge and complexity - a player's ability to deal with new and unclear situations

8.

Knowledge of the Laws - Awareness of how a player's action or circumstance affect everyone's rights and obligations.

9.

Common sense - Exercising good judgment

10.

Suit agreements - Honors alone do not take tricks, ultimately trumps take tricks (see Law of Total Tricks).