Start by choosing a specific topic for your paragraph. In a process paragraph, this should take the form of a goal that will be accomplished once the process is done. A goal that's too broad will make the paragraph unmanageable.
Think about who will be reading your paragraph. Your audience's level of expertise will help you decide how much detail to include in your steps. For example, an inexperienced cook may need directions about how to separate an egg, while for skilled cooks you can simply say how many eggs to separate.
Thinking about the process ahead of time can help make your first draft more concise and complete. One way to brainstorm is to create a list of steps. Include anything you can think of. You can revise it later.
Spend some time cutting your list of steps back down. Delete irrelevant items that will not actually help the reader move toward the goal. Eliminate steps that are too detailed for your audience.
Make sure the remaining steps are in the right order. Add detail to any steps that are too vague for your audience's skill level, and make sure you've included any necessary information about tools and equipment.
Turn your list into a rough draft by putting the steps into sentence form. Use transition words like "next" or "after that" to clarify the order in which the reader should perform the steps.
Edit your paragraph to make sure it flows logically and has clear sentence structure and transitions. Reread it to make sure each sentence adds useful information, and fix any grammar, spelling and typographical errors.
Find a trusted friend, parent or teacher to look over your paragraph and point out errors or unclear parts you didn't notice. Regardless of how thoroughly you edit your own work, having an external perspective will help you make sure it is clear, complete and correct.