Jesus is right but if there is no HOA and the neighbor does not want to co-operate, you can also call the city the property is in and make an official complaint. They usually will send someone to verify your complaint and send the homeowner a first warning with a time to comply. If the homeowner ignores the warning after the deadline is passed, the city will issue a fine (that fine varies depending on the type of negligence.
Such as landscaping? I would contact the HOA if there is one and see if they can tell the homeowner to keep up curb appeal. If there is no HOA, kindly see if they would like any help with the yard work. You never know what problems the homeowner is in. If they are in ddefault, then it will be unlikely they will fix anything. The best option would be to see what their situation is and if they are in default, have a realtor contact tthem and try to sell the property as quickly as possible.