A slightly humid house may not seem like a big deal, but this is one aspect of your home that you really should not let slide. Too much moisture can damage your home; mold and mildew can build up in the structure of your house, which is bad for both the house and your family's health. When walls weaken, wallpaper peels, stains pop up, and bugs will like your house more. And anybody living in that house can develop health problems from breathing in the mold spores. What a charming place to live! There are several methods you can use to manage the moisture levels in your home. Some are cheap and easy, and some are at the other end of the spectrum. Humidity control is easier and cheaper than repairing the damage done after the fact, and is a much better plan in the long run. Just remember not to get carried away; there is such a thing as your house being too dry, as well.
Getting Rid of Humidity
First, identify the source of the moisture in your house. The less moisture coming into your house, the less humid it'll be in there. Some sources of water problems are as simple as poor ventilation—especially in the bathroom—and leaks/condensation from plumbing. These are fixable, although you may have to call a professional if you aren't handy. Some moisture is unavoidable, like condensation in a basement. That you just have to learn to manage. If there is any mold in these areas, clean it up after you've taken out the moisture source.
Good ventilation will lower humidity levels in your home. This is the fix for the bathroom problem I mentioned, and also for cooking areas. A lot of moisture is thrown into the air during your daily shower and when you're cooking up that 5-star dinner, so a fan that vents outside is a good idea. Use them if you've got them, or get them installed. Even just opening up windows for a cross-breeze will get air moving and lower the humidity in the house. Unless it's more humid outside than in, obviously.
Air conditioning is another way to improve air quality in the house. When it's too hot and humid outside to leave windows open for ventilation, turn up the A/C. If you don't have air conditioning already, it'll be pricey to install and run. The cost will change depending on the size of your house, but the air in your home will be balmy and wonderful. So, if your significant other says you can't afford air conditioning, tell him or her that you're just trying to save the family from mold poisoning, which is priceless.
Dehumidifiers will dehumidify your home. A shocking revelation, I know. Also a less expensive way to get the moisture out of the house than A/C. These work using the same concept as air conditioners, except they don't cool your house. Air is pulled from the room, the moisture is pulled out, and the drier air is expelled back into the room. There are numerous brands and types of dehumidifiers, just be sure to get one that's the right size for the space it will need to dehumidify.
Hardwood or tile flooring is better for air quality, too. It's easier to pull moisture from the air than from fibers in your carpeting, so consider changing out flooring. Carpet feels nice on the tootsies, but it holds onto more moisture, and hides all kinds of gross stuff, like dust mites and allergens. If you suffer from constant cold feet, like me, you can always put down some rugs, which are easier to wash anyway. You'll be tackling your moisture and allergy problems with this option.
Home Maintenance vs. Home Repair
Owning a home is a lot of work to begin with, but if you don't maintain it, it's even more of a pain in the ass to fix. If you ever plan on selling, every problem in the house will lower the amount of money you can get for it. So take care of it. If your house has developed a mold problem, or if your new place has one, you've got to fix it. Sometimes a good scrubbing will be enough, but if it's gotten really bad, you may have to replace flooring or drywall. You can either try to do it yourself, or call in the professionals who know how to safely remove the problem and fix it back up. From personal experience, DIY projects can potentially turn into an even bigger mess (or physical injury), so choose carefully.