To achieve cohesion and coherence in your writing, you should:

Plan your writing before you start. Think of the main topic, the purpose, the audience, and the tone of your writing. Make an outline of the main points and supporting details you want to include.

Use a variety of words and phrases to connect your ideas. Avoid repeating the same words or using too many linking words. Choose the words and phrases that best suit the meaning and context of your writing.

Use reference words and substitution words correctly. Make sure they refer back to the right words or ideas in the previous sentences or paragraphs. Avoid ambiguity and confusion for the reader.

Use ellipsis sparingly and appropriately. Only omit words that are obvious or redundant from the context. Do not omit words that are essential for the meaning or grammar of your writing.

Divide your writing into paragraphs with one main idea each. Use indentation or spacing to separate your paragraphs. Do not make your paragraphs too long or too short.

Use signposting to guide the reader through your writing. Use words and phrases that indicate the introduction, the body, the conclusion, the sequence, the contrast, the comparison, the cause, the effect, the example, the opinion, etc. of your writing.

Use topic sentences to introduce each paragraph. Make sure they summarize the main idea of the paragraph and relate to the overall topic and purpose of your writing. Do not include irrelevant or unnecessary information in your topic sentences.