write an effective descriptive paragraph

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1) Find and Explore a Topic
Before you can write an effective descriptive paragraph, you need to do two things:

• find a good topic;
• study the topic carefully (a strategy that we call probing).

For guidelines and examples, visit Discovery Strategy: Probing Your Topic.
2) Draft a Descriptive Paragraph Once you have settled on a topic for your descriptive paragraph and collected some details, you're ready to assemble those details in a rough draft that begins with a topic sentence. You will find a common model for organizing a description at Draft a Descriptive Paragraph.

3) Revise a Descriptive Paragraph
Now you will revise your descriptive paragraph, concentrating on its organization. That is, you will check to see that your sentences follow a clear and logical order, each detail related to the one that came before and leading to the one that follows. These two exercises will give you practice in revising effectively:

• Practice in Supporting a Topic Sentence with Specific Details
• Practice in Organizing a Descriptive Paragraph

4) Revise, Edit, and Proofread You're almost done. It's now time to invite someone else (a classmate, for example, or your instructor) to read your descriptive paragraph and suggest ways to improve it. Taking your reader's comments into consideration, revise the paragraph one last time, using as a guide this Revision Checklist for a Descriptive Paragraph. For examples of the finished product, see Model Descriptive Paragraphs.
source: http://grammar.about.com/od/developingparagraphs/a/descparhub.htm