Simply look up lists of desired features that raise home value, and then consider which if any of those you find undesirable. Bear in mind that many such changes would make a home less pleasant to live in, but some may match other goals than hedonism or convenience. Others, like using a clothesline or removing a lawn, are widely illegal and may require activism to make available. Of course, if you ever want or need to sell your place, all of these changes will make that harder. Choose mindfully.
* Balcony. Only useful if you have a great view or love outdoor living, also often a maintenance hog and sometimes a hazard. Remove and smooth over.
* Electrical outlets. Modern appliances demand many outlets, and using all that crap -- or even just having it plugged in! -- runs up your bills. If you are trying to reduce electronics and their expenses, then remove outlets and smooth over. One per room is plenty for a low-energy home. If you really want to go whole hog, remove ALL of them from bedrooms and use only integrated lighting or fans. This should really kill value.
* Fireplace or woodstove. Can be a fire hazard if not maintained properly, but priceless in a power outage. I don't recommend removing features like this that give you fault tolerance.
* Garbage chute, laundry chute, dumb-waiter, etc. If on the blueprints, smooth over and ignore. If not on the blueprints, you can just cover it with a bookcase and nobody will know it's there.
* Giant bathroom. Homes built in the last decade or two often waste a room-sized space on this. Rip out and replace with a more useful room. Leave a small powder room or 3/4 bath if necessary.
* Hardwood flooring. This is easy to hide by covering it with carpet, linoleum, etc. If you dislike bare floors, carpet will be more appealing to you while still reducing value.
* Hidden room. If you're not using it, this is just larded value. Anything not on the blueprints can simply have the door covered by a bookcase and nobody will know it's there. If it's on the blueprints, break it open to expand another room, or turn it into a lower-value closet.
* Kitchen island. Remove and smooth over. In a small kitchen, enjoy your new elbow room! In a large kitchen, replace with a rolling stand that doesn't count as part of the house and is easier to change if you want something different.
* Laundry room. This highly valued feature is somewhat costly to remove, but if you wish to make Earth-friendly changes such as hand-washing and/or line-drying your clothes -- or motivate yourself to walk or bike to the laundromat -- then it gives big bang-for-buck in reducing value. You can knock out a wall to expand an adjacent room, or turn it into closet space.
* Marble countertops. A fucking nuisance to keep nice, because they chip and stain easily, so you are better off with a solid, durable, nonpermeable synthetic. If you want marble for its cooking features, buy a slab and a rolling pin. Look for dark speckled countertops. In addition to discouraging buyers, and thus lowering value, these hide dirt and stains!
* Open floor plan. While great for a single person or young family, these are terrible for large families that need privacy for different incompatible activities. Adding walls to subdivide big spaces can be costly, but it gives you more walls to hang things and much better sound control.
* Paint. This costs to apply, sometimes a lot, but if you like strong or unpopular colors it can really turn people off. The most unpopular color of all would actually make a great exterior for blending your house into the landscape. If your assessor is not using a sound rubric with points per specific item, unappealing colors can greatly reduce subjective evaluations. This guide lists how much a given color can lower or raise house prices.
* Pet accommodations. Remove, smooth over, and if you have pets use portable things instead.
* Separate tub and shower. Extra stuff to leak or need repairs. Consolidate or omit one. If you hate tubs and never use one, going down from a full bath to a 3/4 bath can really reduce value.
* Skylights. A place looking for a leak to happen. Remove and replace with solid roof.
* Walk-in closet, dressing room, or pantry. Convert to a different type of space, preferably in a way difficult to revert. As it happens, we have a space that was once a porch, then was a walk-in pantry, and is now Doug's glass room. Versatility is awesome to live with, but won't help you kill value. Ideally, you want to remove any shelving and cover the walls with something that discourages using the area as storage space. Portable furniture to make the place useful will not count toward house value.
* Wet bar or butler pantry. For some folks, these are just in the way. Remove and smooth over, or renovate into something else such as storage cabinets.
* Wine room or storage. Remove any wine-specific features and you can then use the space for other purposes.
* Garage. If detached: remove and replace with native landscaping, or turn into another space that cannot easily be reconverted to a garage. If attached: renovate into living space. You can get a bedroom at least, or two if it's huge. This is often very expensive, but much less so than building an extension, so if you want more space it's a great trade. Want to protect your car? Use an awning or other portable feature that won't count toward property value.
* Lawn. Remove and replace with native landscaping. This can be cheap or free if you do it yourself, but more expensive if you hire it out. You may be able to trade good sod for the removal effort. In some areas, you might even get money to replace grass with native plants, but take care that this does not increase the value.
* Outdoor kitchen. Remove and smooth over, or replace with native landscaping, depending on location. If you really want to cook outdoors in an increasingly crappy climate, use a portable grill.
* Patio or deck. Remove and replace with native landscaping. If you dislike outdoor living -- especially if climate change is making that less appealing -- then this is another excellent choice.
* Swimming pool. In-ground: remove, fill in, replace with native landscaping. (Turning it into a pond leaves more value in place.) Above-ground: remove and replace with native landscaping.
* Trees. Especially big old trees, these substantially increase property value. If you are allergic to tree pollen or find a shady yard depressing, you might consider removing them. But this is an Earth-hostile change that also makes the house harder to cool. Not recommended. However, some trees lower property value; standing dead trees are good for wildlife but bad for assessments -- just remove any branches that might fall on something you care about. Evergreens are unpopular too.
Why all the native landscaping? Because most people want a manicured landscape and hate the "messy" look of natives. Planting natives thus kills curb appeal and value, while secretly making the place more attractive to wildlife. Nothing says "fuck off, humans" like a yard full of well-chewed caterpillar food!