。
Nothing is more precious than friends.
Literal
Friends-than important-[attributive-な] things [subject-が] not-exist.
The Xより [attribute]ものはない ('nothing is more X than Y') is the superlative construction — 'there is no more X than Y.' 大切 ('important, precious, dear') paired with もの gives 'precious things.' A classic heartfelt statement about the value of friendship.