It is a shame that many high school teachers continue to penalize students for each occurrence of "one" or "you" in an essay. You certainly are permitted to use these words in writing, but you must do so sparingly, appropriately, and for the reader’s sake. "You" and "your" are somewhat informal but are nevertheless directed explicitly at the reader; thus they are especially appropriate for memos, letters, advice, or a set of instructions designed to apply to the reader in the act of reading:
I am responding to the memo you wrote to me on March 20.
Your first task is to remove the nozzle.
In more formal, technical documents, rely on the word "one" to refer to people generally, ideally as you present them as potential thinkers or doers:
One can assume that there is a threshold axis above which the eyes simply cannot detect the difference between a circle and an ellipse.
Finally, be careful not to switch back and forth arbitrarily between "you" and "one"; be consistent and use your common sense.