I've seen some interesting things during my landscape career. Below is a list of some of the more common issues I see.

Insufficient Slope / Improper Grading

An exposed egress window or lower level walkout is great, but not if it allows water into your home… Be sure there is enough slope to drain water away from your home. Especially if your home is built before the neighbor's you may have issues with grading if you aren't cautious.... there is often a "race to higher ground" when building homes in an area. The first home is built at an apparently reasonable level, but each neighbor wants to be a bit higher to keep water off of their property. The unfortunate effect is that the first person to build often ends up with the water issues.
It’s also not great to make your home look “perched” above the surrounding landscape. Raising the home to have the height needed for an exposed basement can have other costs too…retaining walls are expensive and the slopes you’ve added to you property can be less usable than reasonably flat areas.

Poor Plant Selection

Some plants are poorly suited to home landscapes. They may be weak wooded & brittle, disease prone, spread copious amounts of seed or spread via runners. I love aspens but they are short-lived and have a number of other problems. They can be used in many landscape settings when something is needed to establish quickly, but it needs to be understood that they are best used as a short term solution while other long-term trees like oaks can become established.
Understand growing conditions and soils before selecting the plants. The plant may live, but it won’t thrive. If proper consideration isn't given to sun/shade patterns, wet/heavy soils, drier areas, soil pH etc.
It's also important to pick the right size plant for the space. It's very easy to forget that a shrub will grow to be 9' tall when it's in a tiny nursery pot but it's much better to give the plant plenty of room to grow - especially if it's planted near a home or other building.

When building a patio, walkway, retaining wall, or other hardscape element in Wisconsin, It's critical to create a solid base. Six inches of highly compacted gravel is a minimum for all surfaces. With walls or driveways that depth can double or more. Understanding the soil that your project will be built on top of is important. soils that expand or are high in organic mater cause problems. Also, remember that soils will often settle immediately adjacent to a new home so it might be worth waiting to install some elements immediately adjacent to a home.

Soil on many sites is often either incredibly compacted from construction equipment or has mostly been removed. Plants and turf need sufficient loose soil to live. It's worth ensuring that you have sufficient soil, and that it is of good quality for your purchase. We always recommend a soil sample before installing a new lawn as it's so much easier to enhance the soil appropriately before the lawn is installed.
With any planting (lawn or bed) it's also important to remove as many weeds and weed seeds as possible. This is another area not to rush into. Weeds are much more easily managed before they are mixed in with plantings.

If you need to build a retaining wall, consider that if it built incorrectly you may need to replace it in a few years. Also consider that it will be much more expensive and damaging to the existing landscape to remove the old wall and build a new more suitable wall . Consider the following: you may need to pay to have the old wall material removed. The equipment to remove the old wall and replace it will damage your existing turf and plantings. It may be smart to simply build a new wall in front of the failing one assuming it is stable enough. Boulder walls are very common in our area but few are built so they aren't settling and allowing soil to wash through. Even worse than boulder walls are walls of local outcrop stone that fractures apart after a decade or less.

Basically… the cost of going cheap on the front end far exceeds the cost of doing it right from the start.

I’ve been very impressed with how realistic some of the new artificial stone products look. They are visually appealing, have consistent dimensions (which makes install a breeze), and are often competitive price-wise with “the real thing.” My question is what happens if one piece breaks in a few years and the material is no longer available, or you want to expand the area, When I install a patio that can cost as much as a car I start to think about it the same way I think about my vehicle purchases. I don’t want to buy a car that’s “highest in initial quality”…I want to buy a car that is dependable, timeless, and if something does go wrong, I can find a replacement part…

Remember that it can cost a great deal of money to maintain an elaborate landscape. Discuss your annual landscape budget with a designer before committing to any landscape plans.

Outdoor rooms, subspaces, shade structures and vertical elements like fences and shrub masses can define spaces - making large areas more human-scaled and comfortable. If you can’t afford to include these elements now, consider planning for these elements early so you aren't blocking access and you are not wasting time and money by planting or installing elements where they will need to be removed later.

There are so many small ways to make a difference. Consider:

Managing stormwater / encouraging infiltration.
Planting habitat / not using invasive plants.
Utilizing plants that thrive in the existing conditions without additional watering and inputs.
Using materials that will last year after year and are locally sourced.