New Deck Install Questions

Hello, trying to find recommended process for a new deck installation. The base is already done and I plan to add butyl tape to the joists.

Going to use redwood 2 x 6”s from Home Depot. Since the wood will be new, what prep is needed? If prep is required before staining should it be applied to all sides of the wood or do I assemble the deck and then just prep the visible surface? Same question if no prep is required prior to staining—do I assemble the whole deck and then just stain the visible surface? Thanks!