Should I glue or nail hardwood flooring in several widths up to 6 inches?
I like installing solid wood on sleepers, but it requires an extra 3/4” depth for the floor installation. 

I’d also acclimate the wood to the room for a couple weeks prior to installation. To me, acclimation means separating the boards and spreading them out on the floor...do not leave them bundled. 

Then, I like nailing the boards to the sleepers through the tongue side at about 12” - 16” oc. Stagger the sleepers under the boards and leave about 1/2” air gap at the edges. (I’ve installed boards like this in gymnasiums, but we use thicker boards, thicker sleepers and we leave a 2” gap at the edges. )

One trick to make sure the tongue and groove is milled properly is to hold one board vertically and jam another into the t&amp;g edge. It should fit snug. If it holds and doesn’t slip out, then it’s fine. If not, the boards will wiggle and creak when walked on. Try lots of boards using both edges. 

Oh, we stain prior to installation, but seal after. 

Oh, for best results, install in the dry season...for obvious reasons.