There are a few things that I try to keep in mind for my own readings.
First (and Caitlin Matthews mentions this in her book), there are different levels of meaning for each card. Besides the general associations (Tree = health, Fox = sneaky), we can also use the symbols' literal qualities (Tree = slow-growing or branching, Fox = small furry animal). We can also use many of the cards to fulfill grammatical functions (for example, adjectives: Mountain = big, Child = small, Mice = less, Key = certainly/definitely - and, as Chanah points out, Fox = wrong).
Secondly, as Teheuti reminds us, the cards can be seen as indicating a variety of levels regarding degree of potency (Scythe = paper cut, Tree+Coffin = a cold).
Thirdly, I think it's important to find a happy medium in terms of number of keywords, i.e. not so many that a reading becomes an unwieldy process, and not so few that your vocabulary becomes too limited. A good number of keywords should allow you enough variety so that you don't get stuck. And those keywords should provide some significantly different approaches. For example, having liquidity and independence as potential Fish meanings saves you from those occasions when "money" just doesn't fit. For me, right now I'm finding that three major keywords, along with one to three ancillary keywords which might come up less often, seems to hit the sweet spot.
I agree with danieljuk that we shouldn't feel pressured to jump into the GT. Melissa a/k/a the Sassy Sybil a/k/a tarotmama does a great job in her courses of demystifying the GT and encouraging people to jump in, but I still feel that it can be overwhelming for a beginner. I don't feel like I'm ready to tackle it yet. There's plenty of reading goodness to be had in smaller spreads. I get a lot of mileage currently out of lines of five cards.
At the moment I have a bias against things like mirroring and knighting. Sometimes it seems like the point of all these techniques is to combine every single card with about a third of all the other cards in the GT. I like to keep it simpler. Of course, that's only how I feel right now - I reserve the right to change my mind!
