Mistakes will always be made in French, and now you can learn from them.
Wrong: J'espère que tu sois
Right: J'espère que tu seras
Explanation: It's perfectly logical to think about what espérer means - to hope - and to reason that it should be followed by the subjunctive, like vouloir (to want), for example. Unfortunately, French is not always logical, and j'espère que tu sois is just plain wrong. Espérer not only doesn't take the subjunctive when used in the affirmative,* it's not usually followed by the present either. If whatever you are hoping for is in the present or future, you should use the future: J'espère que tu seras content (I hope you'll be happy) or J'espère que ça ira mieux (I hope things get better). If it's in the past, you use the past: J'espère que tu y as réussi (I hope you succeeded). But you can never say "j'espère que tu sois."
*Espérer does, however, take the subjunctive when it is used negatively or interrogatively.
Related lessons: French subjunctive | Stem-changing verbs