The positive/neutral/negative thing is something I'm constantly fine-tuning. There are several ways to approach it.
The most obvious one is polarity: Wands and Swords are positive and active; Cups and Pentacles are negative and passive (as are their underlying elemental correspondences). That gives them a certain quality of assertiveness on the one hand and receptivity on the other.
A second way is numerical: odd numbers are active because they are seeking balance, even numbers are passive because they are trying to maintain it; this balancing act is constantly in flux, never static for long.
A third way is by Tree of Life correspondence: Minor Arcana cards that represent numbers high on the Tree and centered on the pillars are more positive, those that are lower on the Tree and off-center are "tainted" by impure and unbalanced exposure to the material world and therefore more negative.
As a fourth way, there are also some Pythagorean attributions (One is the monad or point, all potential and no direction - a place to begin from but not an active expression in its own right; Two is the duad or line, the first impulse to strike out from the center - it shows linear reciprocity like the action of a pendulum; Three is the triad or surface, showing the two-dimensional plane scribed by rotating the end of the line around the center - thus the idea of progress and development). These correspondences go up to 10 (and beyond) but in my opinion they start to wander away from what is useful in tarot interpretation after 5 or 6.
The small cards that I made negative (5, 7, 8 and 10) and positive (Ace, 3 and 6) were for qabalistic and numerological reasons; 2 and 4 I made neutral because they're limited in their growth potential and range of motion, while the neutral 9 relates to the variability of the lunar cycle.
With the court cards, beyond their suit associations, I decided to make them all neutral since any one of them can be "all things to all people." If they are reversed or ill-dignified elementally, I shade them toward negative; if they are adjacent to and supported by positive, energizing cards, I shade them the other way.
For the Major Arcana, I just made some semi-arbitrary decisions: The Fool, the Magician and the High Priestess I made neutral because they operate at an abstract and rarefied level that is kind of above mundane considerations of positive and negative; the Empress and Emperor I made positive because they are actively established in the fabric of everyday existence; any of the cards that imply value judgments I made neutral because those can go either way. The negative Trumps are the obvious ones from standard usage, but I added the Moon because of its illusory "false light" connotations. The other positive Trumps are also all of the "usual suspects" plus a couple whose astrological associations seemed to merit it.
Deciding what should be neutral was the hardest call. I hedged my bets by saying they can take on the coloration of adjacent cards to a greater degree than the solidly positive and negative cards.
I see the "driving" card in a pair as being the one of greatest potency, either positive or negative. Some are obvious, such as a Trump paired with a numbered suit card, while others take more careful judgment to determine. I always look for the one that seems to be in a controlling position or has the most to say about the matter. Sometimes a single card can be the "driver" for an entire spread.
As far as resources, the best book on numerological (actually "occult number theory") qualities and correspondence is Joseph Maxwell's "The Tarot." Crowley's "Book of Thoth" covers what I call the "descending energy model" of numerical and Tree of Life correspondences - basically "Ace good, Ten not so good." Liber Theta (free from the College of Thelema) is an adaptation of the Golden Dawn's Liber T that provides more accessible qabailstic material than Crowley. Although it's not about tarot and gets a bit too "religious" for me, Agrippa's "Three Books of Occult Philosophy" has some number theory stuff that is useful. I don't know of any good books that cover putting it all together in a reading.
ETA: I don't have this one, but I understand it's good.
http://www.amazon.com/Tarot-Decoded...ue&ref_=ox_sc_sfl_title_42&smid=ATVPDKIKX0DER