What is the best way to "clean" the wood on a weathered oak
threshhold?

I plan on refinishing it but the wood is now dirty and grey since the
old finish has worn away.

I could always aggressively sand but I was wondering whether it made
more sense to combine sanding with some type of cleaning or bleaching.
I don't want to bleach away the wood's natural color, just remove
accumulated weathering and embedded dirt.

So would you recommend cleaning in addition to sanding?
If so what chemicals and/or combinations? (bleach? oxalic acid?
hydrogen peroxide? other?)
What strengths?
Any suggested brands?

Thanks,
Jeff