A home that isn't being maintained like others in the neighborhood can negatively affect your visual sense of appeal and in some extreme cases, even affect property values. It might be an overgrown yard, a fence in need of repair, excessive noise, unruly pets, paint peeling on the home or even a car or boat parked in front of the home that hasn't moved in weeks.
Most people want to be good neighbors and may be willing to correct an issue once it is brought to their attention. A practical, but possibly confrontational, solution is to contact the responsible person and describe your perception of the issue. However, they may not always agree with the same urgency and it might be necessary to seek other remedies.
An owner-occupant may be more sympathetic to the neighbors and willing to correct the issue. If you think the home might be a rental property, check with the county tax records to identify the owner. They may be unaware of the situation and welcome the notification to protect their investment.
Another alternative might be to notify the homeowner's association, if there is one. One of the benefits of a HOA is to enforce community appearance standards as set in the covenants or bylaws that specify how properties must be maintained. This could be a less personal method of reaching a beneficial outcome.
If the source of the problem is a code or housing violation, the city may be the ultimate authority. Most cities have a separate code and neighborhood services division and some cities have 311 for non-emergency assistance.