New/old wood. How to proceed?

You should use a stain stripper to remove the dark brown stain as much as possible the brighten. Restore-A-Deck Stain stripper should work. After I would look at the Armstrong Clark in a Semi-Solid color.

Thanks for your reply.

Actually, that's not dark brown stain. I took the photos on a cloudy, rainy day.

Here are some taken when it's dry. There's some residual stain, but for the most part, it's pretty dirty and weathered.

Would power wash be okay, or does it require stripping/brightening?

Thank you for your consideration.

Stripping and brightening would be best and much easier.

Thank you!

Welcome, please post some pictures after the cleaning.