Paint Prep. Small Areas

Howdy everyone. For those whom have painted their own aircraft: how did you prepare the areas like the wings rear spar between wing and aileron/flap? I would think those areas would be difficult to get in and sand. Other areas of concern?

Much obliged.

Those areas I usually wash really good with scotchbrite and soap then scotchbrite and etch. They are pretty protected and don’t get abused.