An altar is any surface or space that you designate specifically for your spiritual practice. You can use any size table, shelves, counters, or any space that will not be disturbed or used for any other purpose than spiritual work. Your altar is personal and does not have to follow any set structure unless you follow a specific religion that requires you to do so.
I have had altars in pretty much every room of my house throughout various stages of my life. Growing up, my family had an altar on the foyer table by the front door, but as a teenager my altar was on the top of my dresser and, later, on my bedside table. After moving into my one bedroom apartment that I shared with my boyfriend, I set up my altar on a single shelf of one of my book cases. As I unpacked, it migrated to a shaded windowsill in our bedroom. Now that I’m in a larger house I’m fortunate to have an entire room dedicated to my spiritual practice that is only shared with my creativity (it takes up a surprising amount of space) and one of my snake familiars. I do have a tendency to set up smaller, more informal altars around my house as well.
The important thing to remember is to use the space you can spare rather than taking up space that you need. If that means having an altar that can be packed away into a box or stored in some other way, so be it.
Before you begin, get yourself in the right mindset. Cleanse yourself in whatever way you wish and ground out any energy that may distract you from your purpose. Remove everything form the space you want to use for your altar and physically clean the space before you energetically cleanse it.
To energetically cleanse the space, you can use Florida Water or Seven Sacred Waters to wash hard surfaces or spray them onto soft surfaces. I wash my laundry with Florida Water, so all of my altar cloths are energetically cleaned during laundering. You may also use smoke from sacred herbs such as cedar, rosemary, lavender, etc. Some people opt to use incense as it is convenient and easy to burn, but make sure that the incense you're using are made from pure ingredients, not fillers.
I like to start with a clean altar cloth, but you do not have to use a cloth if you don’t want to. To me, an altar cloth is like putting on clean underwear after a shower. It might not be necessary, but it’s still nice. Add anything you deem necessary such as representations of the elements, deities, ancestors, etc. Candles are a nice touch whether you are using them as a representation for fire, spells, or simply adding to the atmosphere of your altar. Natural light such as the glow of a candle, the sun, and the moon are perfect for getting you in the necessary mind-frame for spiritual work. Crystals and stones hold a special place in my heart. I’ve been including them on my altar for my entire life whether it was a simple river rock, quartz point, or piece of jewelry. I worked around crystals as my profession for so long that it was difficult for me to ignore their energy and magnetism.
It’s a good practice to change or update your altar throughout the year whether you have a nature based practice or not. A stagnant altar is not a functioning altar. That means you need to dust your altar and sacred objects regularly. Straighten as needed including ritualistically disposing of offerings that may be past their prime - I like to announce to whoever the offering was for that I’m removing an offering from my altar. I typically only put biodegradable offerings on my altar, so they are usually buried or left outside in a secluded spot where nature can take it’s course. Add new offerings or relevant objects on your altar as you feel called to. I will sometimes leave the tarot or oracle cards that I have drawn that day on my altar. If you do not feel mentally and spiritually up to the task of maintaining your altar, wait until you feel better. It is okay to stray from your path, in fact, it is completely normal. No one is perfect and we all have our struggles.
Just remember, your altar is completely your own. It doesn't have to be aesthetically pleasing or large. The important part is that you make sacred space for yourself. It will drastically improve your spiritual practice no matter your path.