I have done all these projects on my own and with friends in the past:

1. A $30.00 gallon can of paint is worth $3,000 on the walls. Paint!
2. New baseboard & Crown Moulding
3. Remove carpet & replace with snap in place engineered woood floors
4. New Tile
5. Update Kitchen cabinet hardware and appliances
6. Update your windows
7. Install ceiling fans
8. Re-sod the lawn, plant fresh flowers in the yards or go native plants and low water consumption.
9. Update the vanity, sink, light fixture and toilet in a bathroom.
10. Steam Clean the carpets

Declutter, deep clean, paint, deodorize, add flowers, landscape cleanup, if they have hardwood under the carpet remove the carpet.

Fresh paint actually.

Get rid of 1/3 of the furniture/knick knacks in a room. Most people have just too much stuff. 

Polish up those hardwood floors or get new carpet.  Forget about those crappy snap in floors. 

What you can see? 

Paint inside/out

What can you feel?

Hardware and other finishing touches.

What can impress?

Cleanliness in all aspects and simple yet well-manicured landscaping. 

Richie Alan Naggar hit the nail on the head. See what I did there?  LOL 

Painting works like a tonic...Cleanliness just sparks...Light fixtures with bright lighting...Flowers, garden and stone/rock trim path to front door

Any old light fixture  has to be replaced ...Toilet & seat a must

Knobs and handles...Screens...Window coverings...concrete cracks...a/c vents

Landscaping

Some of that depends on the homeowners and how skilled or handy they are...or who have friends who area. De-personalizing is a big deal and they have to move anyhow. Painting in neutral tones where needed is a cheap and easy fix. It's pretty simple to improve the curb appeal with trimming or removing plants, adding plantings, cleaning up that front door (paint, welcome mat, workable door lock).

if you are going to DIY you best stick to paint, updated lamps and shower curtains.  Beyond that my best advice is hire a professional.

Painting and having a clean place I think are #1. Any touch ups if needed such as caulking or grout is missing.

The easiest and cheapest improvment is to convert your lights to LED. There are all types of bulbs and fixtures available that allow any homeowner to make this change. Even flourescent bulbs can be upgraded just by cahning the tubes.

Murals on the walls depicting their childrens acheivements.

Maintance free front yard filled with native flora planted 4 years ago.

And of course...chain link fence.

That is how one describes a career listing.

To answer your question, "The opposite of ALL of those."

Painting and cleaning up for certain!  

flooring

Thomas J. Nelson, Realtor e-Pro, CRS, RCS-D, Vets has it covered well!

After decluttering and deep cleaning, I think new faucets, light fixtures, door and cupboard knobs, and paint make a nice difference. 

It really depends on the ability of the home owner to d it right. I would rather they did not oant if they were also going to get that paint on the floor, ceiling, wondow and even switches. Cleaning the home is worth a ton as well for those those with no DIY skills. 

Rip the fluorescent lights out of the baths that look like a morgue Debbie Gartner . Lighting in a clean home with no smells and mowed lawns can make the difference to stand out. In small rural markets its get rid of dingy paint and paper, the Mopar glow in the dark colors. Broken glass, ceiling roof leak stains don't make a buyer warm and tingly.

Check out Debe Maxwell, CRS article on a home she just re-did and sold. I see that it has been featured. She did an awesome job all the way around - not just the re-do but realizing a more than expected (or dreamed of) profit for the seller. What she accomplished is what buyers in my area are looking for and we've done a bunch of them over the last number of years.  Style/colors/decor may change a bit over time but they all seem to want that clean and clutter free look - light and bright.

Fix, Clean, and paint

New appliances in kitchen make a big difference in some cases. Certainly painting if there is funky wallpaper for example. Exterior painting if there's weathering. New front door.

A fresh coat of paint.

Declutter.

Clean, clean, clean,

It starts with front yard landscaping, manicured grass and added colored flowers.  Next is cosmetic repairs from the entry to the back door.  De-clutter and then the backyard.  Paint where needed as well.  Spend as little as possible but get the house in ship shape.

LOL I just shared a post with some updates done to a seller's home that sold it in no time! Of the things that can be DIY:

1. Change out door knobs, hinges and locks on doors...OR you can actually buy metal spray paint - I used that on a few door knobs and it worked beautifully!

2. Replace the cabinet knobs and hardware.

3. Paint the walls neutral - makes a world of difference. Paint the shutters and doors.

4. Pick out faucets and lighting to have ready for a plumber & electrician to install when the Stay-at-Home Orders have been lifted!!

5. Landscaping - give it a face lift including having colorful flowers in pots by a freshly painted front door.

6. Powerwash all sidewalks, patios and the driveway.

7. Clean windows.

8. Clean out closets.

9. Clean the garage - donate, donate, donate!

Pressure wash the curb in front of your house, pressure wash your driveway.  

Declutter, clean up, including outside and landscaping; touch up paint.

1. Get rid of half their stuff 2. clean deep scrub clean again 3. paint neutral and I mean don't paint it grey - that style is 2017 4. fix all broken or eyesores and health and safety code violations 5. how much money do they have vs total value of house? Super jumbo it's okay to update flooring from old smelly carpeting to wood