You don't really think diamonds are breaking 3-2, do you?

In any case you should prepare for the possibility of a 4-1 break (28% more often for you) that they may not.

Your first three plays should be the king-ace and a club. If clubs are 3-3, dummy's fourth club is your ninth trick no matter how the diamonds divide. Ditto if East has two club honors, doubleton, the actual case. When you eventually lead up to the nine, West can step up with his honor, but once again the C9 is your certain ninth trick.

If the clubs don't come in, you can always fall back on diamonds being 3-2. If you attack diamonds before clubs and find diamonds 4-1, you won't have the dummy entry to set up your 9th trick in clubs.

THE BOTTOM LINE It's not always necessary to attack a likely running suit immediately if that suit provides the only entry to another suit that can safely be attacked first