It is very simple.
Instead of writing full text in the beginning itself, write 2-3 lines summarizing the message you want to convey by each paragraph. While writing the full text, just expand these lines. Make sure that the content you add to each paragraph adheres to the final message of the paragraph.
To manage the theme of the whole paper, just write the messages of each paragraph and read them all together. You will get a clear idea of whether or not the paragraphs follow a single theme and story.
Instead of writing full text in the beginning itself, write 2-3 lines summarizing the message you want to convey by each paragraph. While writing the full text, just expand these lines. Make sure that the content you add to each paragraph adheres to the final message of the paragraph.
To manage the theme of the whole paper, just write the messages of each paragraph and read them all together. You will get a clear idea of whether or not the paragraphs follow a single theme and story.