Failure is the first step toward success.

شكست، گام اولین اولین گام نسبت به به سوی موفقیت است

"Toward" can be translated different in various sentences.

In the sentence above, "toward" is meant "in the direction of"= به سویِ

You meant "in relation to" =  نسبت به  that it's better to use in a phrase like :

An optimistic attitude toward the future.

یک نگرشِ خوش بینانه نسبت به آینده