” Dans l’avenir, j’espère obtenir de bonnes notes à l’école et réussir dans la vie “

Depending on what you want to tell, ” à l’avenir ” may be more correct.

You can trust me as I’m french 😉

To be more precise 😉

“à l’avenir” has the following connotation: “It hasn’t been the case in the past, but from now I will make my best for it to be”. = example here: I used to have bad grades, but it is going to change.

“Plus tard” may also be used, it is used towards a time you can’t exactly imagine, or at least you haven’t reached yet. Example here: I’m not going to school yet, but when it will be the case, I wan’t to have some good grades.

Hoping it has been useful 🙂