Skylights, sliding patio doors and enlarged windows all increase saleability. Get as much space out of the home as possible. Those in older homes may have to be rebuilt or opened up again. On other improvements, opinion is varied. Some homeowners finish off their basements as a rec room but unless they are done properly and not on the cheap, only then can they add value.
Central air is a great seller in the summer months but otherwise is little appreciated.
In-ground swimming pools fall into the same doubtful category. You may put one in for your own enjoyment but many buyers will see a pool only as a costly nuisance, robbing them of their backyard and peace of mind. One final tip. Concentrate your renovation money on the interior, rather than the exterior. That's where the heart is.