After having read the text at least a couple of times to familiarise yourself with it, divide it into sections and examine how it is built.
Firstly, look at where the introductory, core and closing arguments are and how they are connected to one another.
Then, divide it in micro-sections and look for noticeable features that can tell you more about the way the author is using language and style to convey a certain idea.
Examine:
-The length and degree of complexity of the sentence and the presence of recurring adverbs and adjectives.
-The vocabulary used within the whole text (formal or informal, figurative or literal) and whether there is a change from one to the other.
By looking for and providing a critical discussion of those noticeable features your textual analysis will be great!