If you have recently bought a new house and you don't think the previous owners maintained it well, there are some areas that you want to have cleaned before you move in. If you can see easily when you walk through the door that the owners weren't great at cleaning the surfaces and areas that are easy to get to, then it may be safe to assume that the internal components of the home weren't cleaned either. Talk with service providers about getting these different areas thoroughly cleaned and looked at.
The ducts throughout the house collect dust and debris when air settles in the vents, and also when air gets pushed through from the furnace. Mold spores, fecal matter from rodents and insects and other things can hide in the ducts.
Having an HVAC professional (like Bill's Heating & Air Conditioning) clean the ducts will help prevent dust problems, it improves the quality of air, and helps eliminates dust and allergens that can trigger asthma attacks and also allergy irritation. Duct cleaning also improves airflow around the house to help with efficiency.
Does the waste in the house go to a septic tank? If so, you should have septic tank pumped out so you know you are starting with a fresh tank. You can also have the tank cleaned and checked for cracks or flaws, to prevent or avoid unexpected damages in the future.
The drains in the house could be filled with hair and debris from the homeowners that resided before you, and when there is a clog it's that filth that starts to rise in the sinks or tub. Have the drains cleaned so all of the traps are open and so the drains can flow smoothly. This can also prevent odors from lingering out of the drains, and it can prevent clogs later on when you own the home.
If you can easily tell the homeowners didn't clean a lot consider having the carpets and the hood exhaust cleaned by professionals as well, if you don't have the tools to do it on your own. It's easy to see that things are dirty on the outside but unless you get professional help, you won't know what areas need to be cleaned on the inside. You entire HVAC system like the furnace and air conditioner may need to be serviced, along with your plumbing system throughout the house.