There are several simple rules.
Rule number one: declutter. You don't need that much stuff. You don't need all these clothes, and children could do with less toys. It's a good idea to regularly go through your closets, cupboards, storage places and house in general and remove things/clothes/gadgets/old magazines and the like which are out of date/broken/not used within a year. If they are still functional, you can give them to your family or friends or donate to the charity store, otherwise just throw them away. The less stuff you have, the easier it is to take care of it.
However, decluttering is not only about material possessions, it's totally possible to clutter your schedule and your life with too many hobbies or activities, so that there will be no time for the necessary things around the house to be done. Streamline your schedule and don't try to do everything at once. Choose one or two hobbies which you particularly like and let the rest go.
Rule number two. Don't let things pile up. My stress level became considerably lower after I adopted a very simple rule of always washing up the dishes right after a meal or any activity in the kitchen such as baking a pie. You may shove dirty clothes or things which need ironing out of sight temporarily, but in your subconscious you'll know they are lying there waiting for you and it will absolutely stress you out. Teach the children to clean after themselves right away, too.
Rule number three: prioritise. Every household will have its own priorities.If you've just had a baby, taking care of him will be your priority. If you are a homeschooling mother, than your children's education will be your priority which means that you probably won't be able to do some things other ladies are doing. It's OK, as a homemaker you have to attend to the needs of your family which are/may be different from others.
Those three rules above are the very basics of stress reduction, but there are several other things to keep in mind while trying to reduce stress around the house.
Don't try to be someone else. It becomes especially tempting with the abundance of homemaking blogs out there which have the tendency for some women to substitute day time TV and the reality shows. You may follow the blog of that lady who is an experienced cook/gardener/homeschooling mother of 14 children/fitness freak/fill in the blank and try to be like her, but you will never succeed. One man's meat is another man's poison, they say.
You may have a busy family and no time to engage in gourmet cooking. You may have no green thumb. Your health and your husband's income probably won't allow you to have 14 kids and so long and so forth. Realise that on the net people more often than not show only one side of themselves: the best. The lady who spends 5 hours in the gym every day and has great figure may very well have a very messy house, but you won't know because she'll never tell you. The one who spends hours in the garden and wins competitions has a maid who does her housekeeping etc etc. Adjust your life according to your social position/income/health and the like.
Don't live a lifestyle trying to reenact the past in your own home. It's OK to be inspired by Victorians/Edwardians/Little House On The Prairie/I Love Lucy and whatever makes you happy in general, and you can certainly learn good things and moral values, but realise that we live in the 21st century. Some things stayed the same (both I and Lucy use vacuum cleaners), but some things changed for better or worse. Take clothes, for instance. It's still possible to look modest, dignified and feminine with styles available on the market, you don't have to recreate vintage garments or wear girdles.
The same goes about other homemaking aspects. You are not less of a homemaker if you don't grind your own flour or don't make your own washing powder. It's not that it's wrong, but you may have no time for it at this point in your life. It's not wrong to use modern conveniences when necessary.
Plan the beginning and the end of your work around the house. As you get older, you'll need more time to relax and recuperate. I read somewhere that a man can only do 6 hours of really productive labour every day, before he loses his concentration and his drive. That's why it's so important to prioritise and to plan your day accordingly. There should be an hour between the day time activities and the dinner when you call it quits and just relax and sit down with a book/crayons/needlework and enjoy life. Home is not a factory, you can always move some things to the next day.
Delegate the tasks around the house/use help. You should not boss your husband about (think of the infamous honey-to-do lists), but you can and should teach your children to help around the house. If you can afford a housekeeper and you really have a lot of housework, than hire her and don't let anyone make you feel ashamed.
Finally, simplify and minimise. Don't plan elaborate 5-course dinners, unless it's your hobby, of course. Don't overschedule to the point that you are exhausted, overwhelmed and have no time to enjoy life. Remember, life at home should bring joy, not stress.