There are a lot of rules to J, but you can still take on advanced problems in J before you understand all of them. This is a guide on keeping a simplified approach.
Shape Processing
The simplest sentences in J are a sequence of monadic verbs applied to a noun. f g h y is just like the traditional languages f ( g ( h ( y))) form.
Noun shaping is the act of transforming data from an initial from through various intermediate forms just to confirm logic and finally into an answer, and solving such problems in J can still be easier than familiar languages due to its array processing features.
The big advantage of noun shaping is that by not creating verb phrases (sentences without nouns -- sentences that return/are a verb), you do not innadvertantly create trains.
The Vocabulary help page is coded such that Conjunctions are in bold, and adverbs are in italics. Conjunctions bond differently than verbs, and knowing what part of speech your functions are is, essential to using them coherently.
Sticking to Monads
Monads are much simpler because,
1. you need fewer parentheses
2. trains have different behaviour in monad and dyad cases. As do key conjunctions:
Make Adverbs instead of Conjunctions if possible
Conjunctions interupt the "normal" bonding order of sentences. Adverbs will feel like a monad in terms of sentence flow. Not requiring differing parentheses than if it were a monad or dyad.