Generally speaking, the rooms in our homes have to be multifunctional, but it's not always easy to design with all those functions in mind. Whether you're starting from scratch or trying to make the most of what you've got, making a checklist is one of the first things that you should do to make sure your room satisfies all your needs.
To create this checklist, don't think about aesthetics, the furniture or materials you have at hand, or any particularities of the space. This list is simply about figuring out what you want out of a room; how to get there comes later.
There are different sorts of needs to consider, and you should take them all into account while you make your lists. I'd suggest approaching them each individually, although they will naturally speak to one another in the end. Also, for your first pass through the list, write down everything that comes to mind. Don't filter.
If you live with other people, you can each create a list, and you can compare and discuss once you're done. Eventually, you'll have to come to some consensus, but don't try to come together from the start. The differences may be illuminating.
First, there are functional needs. These answer the basic question, "What is the room for?" Some of these kinds of needs include reading books, conversing, watching TV, smoking, dusting, sewing, painting, listening to music, mixing drinks… you get the idea. Be extensive when making this list, though. Nothing is too small for consideration. Identifying every last need will go a long way to making sure that the room truly fits your lifestyle. My sample list for my office was about 80 items long. There's no shame, and really, you'll be surprised with how many different things you actually do in your home.
And remember, it's important to be honest here. Don't think about what most people use their spaces for. Think about how you use your home. If you curl your hair in the kitchen, include it. If you don't cook and would prefer to use the extra kitchen space to store shoes, include it. Simply think about what you want the room to do.
Secondly, there are financial needs. The most obvious of these considerations is a basic budget. If you are starting from scratch, then figure out how much you're willing to spend. Or, perhaps you have no money but want to rearrange the things you have so that your home is more functional. Either way works, but it's good from the get-go to know your limits.
A less obvious consideration that comes into play with finances is that you should think about how long-term you want your design to be. Will these changes last through your child's baby stage, toddler stage, and childhood? Are you looking to keep the space the same through the empty nest stage? Or are they shorter term? For short term solutions, your method of investment will probably be different. You'll want to put money into the items that you can take with you or that you can repurpose, not ones that are highly specific to a current need.
Next, there are physical needs. If you have a young child, you will need to incorporate safety measures like outlet covers and a mindfulness of sharp corners. If you have a disability, you may have certain accessibility needs that will have to be taken into consideration. If you have bad eyesight, you may need to accommodate that with lighting or adjusted distances between furniture. For now, just list these considerations, and don't take too much time thinking about concrete ways that you could accommodate them. This will become clearer when you consider them alongside the other lists of needs.
Finally, there are psychological needs. How do you want your room to make you feel? What kind of atmosphere do you want? Calm, energetic, tidy, fancy, casual, happy, moody, romantic? Again, don't think about what others might expect from a room; if you're designing a front room, some might expect it to be formal, but if your family has four dogs and you never entertain, then you might cherish a room that is more casual. Focus on what you want, since you will be the person experiencing it daily.
Now that your uncensored lists are complete, you can start to use them. Ideally, your space would be able to incorporate all of these elements, but few of us live in a dream home. That said, don't give up on them too easily. With some ingenuity, often in the form of space planning and storage, you can accommodate most of your needs. With the functional needs list, if you truly feel that you can't incorporate all your needs, then go back and rank them according to importance. Use a few different colored highlighters to assign priority. If you paint once a week, then you very well may need a designated space to paint. If you paint once a year, then perhaps you can find an alternate place to keep your gear.
With the emotional needs list, try to see whether there are any conflicting adjectives. Do you want an energetic space that is also soothing? Try to figure out whether you can accommodate both (perhaps with multiple lighting set-ups, brightly colored paintings in a mostly white space, etc.), or if one is clearly more important to you.
Then, once you have your lists tidied up, bring them together. The space should develop organically out of the needs instead of having your needs shoehorned into the furnishings. Chairs for conversation, storage for toys, a flat surface for crafts (which could double as a space for the kids to do homework), ambient lighting for mood, but an extra reading lamp for the times you want to fall deep into a book—the functions will help you determine what kind of furnishings you need.
After making these lists, you will still have plenty of decor freedom with color, style, and layout, but you should have a clearer idea of how you want all those elements to come together. By thinking about your needs, apart from any aesthetic considerations, it is easier to develop with a space that will be functional and that will create joy, instead of one that is simply beautiful.