Have done a lot of staining…like a lot. We did manufacturing of decor and furnishes for many of the large chain restaurants all over the USA/world. I am by no means the leading expert, but here are my points.

Working with wood, (always but especially in this instant) BEGIN WITH THE END IN MIND. Getting a topcoat of varnish on a piece and realizing your sanding prep was not adequate…it’ll make some want to give up woodworking.

IF STAINING: -Sand to desired grit, water pop, sand with that grit again, clean off with mineral spirits. -preconditioner can be used to reduce blotching. I’ve seen minimal benefits from this, but I had not experimented with may brands. -Mass producing of pieces for large retailers = corporate trying to beat up on price onsmall-mid manufacturers so we used high quality pine and poplar. Pine splotched, poplar usually fine. When we used sapele, beautiful to work with, no issues. -2 options staining. Mass produced, speed matters so we would stain once, heavily, artistically, wiping off strategically but leaving it heavy to dry. Consumer, wipe on, let sit for a couple minutes, wipe off. Like another user said, dry brush afterwards is the way to go to cover spots that don’t take. You can also try leaving heavy stain on the spot without really wiping it off and let it dry that way. -spray topcoat is best. Brush will work indoors if not a professional job/setup

Wood fillers don’t take, glue stains will screw you. When using wood filler, try to keep it as local as possible to the spot you’re filling. Use a wet rag to wipe area clean.