Quite many conlang grammars I've read start by introducing their alphabet, their writing system and their vocabulary, and leave the grammar for the very end. This is often frustrating: what I'm interested in usually isn't the alphabet or choice of words used by the language, and the interesting stuff (the grammar) is introduced using all the vocabulary that I'd like to skip (bridi? selbri? and don't get me started about ithkuil...).
I wonder why conlangs are never described the other way round. You could start with the grammar, explaining how to build valid ASTs and their meaning, and represting the ASTs with s-expressions and not sentences with complicated morphology and vocabulary. Then, you can get on with the rest, but it would be great to have an idea of the grammatical workings of the language before worrying about how it is actually written or spoken.
In other words, it is one thing to describe the grammar of your language using ASTs, and it is another thing entirely to describe the real syntax of your language which will serialize the ASTs into written or spoken sentences; in my opinion, things should be done in this order.
[The same goes for programming languages: when trying to invent a language, it is tempting to start with the details of the syntax and keep the hard business (the grammar) for later, whereas I think it would be more productive in most cases to start with a Lisp-like syntax, think about the grammar, and optionally invent a specific syntax later.]
Of course, in the case of conlangs, you could object that you cannot describe the grammar without introducing at least some words of the conlang. I mean, your conlang is likely to have some basic grammatical words with no English equivalents (what would be the point, otherwise?) and you would need them to describe the grammar. Even in this case, things are likely to be more readable if you use a short English periphrase instead, but, if you really can't, using specific words is reasonnable. However, this does not mean that you have to use the same words as in the final syntax in your language! For exemple, assume that your language uses declension, and has a case called "baritive" and a word "foo" which means "sheep": don't explain how the baritive of "foo" is actually "bazquuux" for convoluted reasons, just write "(baritive sheep)".
Most importantly, you should not start with real world words. It's hard to think of an interesting way to come up with words for the various kinds of animals, fruit, colors and the like; if you just say something like "(attribute (any [violet]) [color] [blue])" instead of "PéargnH i'ch'bẃļorthnutŝb", I really won't mind.