Excellent answer from Maureen.
Just a few extra thoughts: Examine the property and see if anything sticks out like a sore thumb. Most likely, it'll be the kitchen or baths. But sometimes there's something else that's also a real turn-off. For example, most buyers won't look past walls painted purple and the green shag carpeting to admire the new baths.
Spend at least some on landscaping and curb appeal. It's surprising (to me, at least) the number of potential buyers who reject properties without ever getting out of the car. Spend the money to get them out of the car and into the property.
And while the question is reasonable--return on investment--recognize that's not always the goal. Listen: Does ANYBODY need stainless steel appliances? Of course not. Same with granite countertops. But a large number of people will reject, out of hand, houses in which the kitchens don't have stainless steel appliances and granite countertops.
So, do stainless steel appliances offer an attractive return on investment? No. But what they will do is broaden the market of potential buyers to include those who've put stainless steel appliances on their "must have" lists.
Hope that helps.