Thank you for the opportunity to help you with your question!
Your instructor is correct you never start a process essay with you. When we think of a process I suggest that you write it down in steps on paper.
In order to start the process without using "you" it would grammatically correct to use the following recipe:
Get the invitations to those whom you choose to invite
Go to the bakery and get a cake.
If you notice these statements are in the affirmative, more like a command. For instance when you want a child to do something sometimes you will say please or when you want to be firm with them you would use an affirmative command statement. As far as a thesis statement it is an essay so you would simply say something like In order for a person to a have a successful surprise party a person would do the following. Do not just list how to have a surprise party each step should go into detail as to how you have a successful birthday party.Please let me know if you need any clarification. I'm always happy to answer your questions.
Please let me know if you need help with your assignments in the future.
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