One of the rules of academic writing is to regard the paragraph, rather than the sentence, as the basic unit of the essay. Each paragraph of argument should only contain one main point, which is discussed and explained during the paragraph. Paragraphs of illustration might contain several points, but these will relate to a main point stated in this way in a preceding paragraph.
This means that you need to structure the argumentative paragraph as you would a sentence, so that the reader can take it in as a whole - this also implies that the paragraph should not be too long. Like sentences, you can think about paragraphs as following a basic pattern: after a sentence (or clause) which connects the paragraph to the one before, you state your main point in one self-contained sentence, and then follow it with one or two sentences of discussion and illustration which rephrase the main point and bring out different aspects of it. Drawing out your paragraphs in this way can be regarded as one of the strategies for defeating writer's block - although it may seem repetitive, it is in fact a highly effective way of taking the rhetorical situation of your essay into account, since it does not assume that your main point is obvious to the reader.
It is useful to think of sentences within a paragraph of argument as belonging to a hierarchy, or logical tree, similar to that of outlining, which is a technique which could be used to organise paragraphs if you feel the need to lay them out sentence by sentence. The sentence containing the main point corresponds to the top level of the tree, a sentence illustrating or modifying the main point belongs to the next level down, a sentence commenting on an aspect of the main point goes in the level below that, and so on. During the course of the paragraph your sentences should move both down and up the tree hierarchy - it's often effective, for example, for the concluding sentence of a paragraph to move towards a greater level of generality than would be appropriate for the detailed commentary of sentences in the middle.