An altar isn’t a stagnate thing and as such should be cleaned and worked with regularly. After all, if you had family coming for a visit you wouldn’t want them sleeping in a guest bedroom crawling with spiders & roaches, and coated with inches of dust. If you are fortunate in that you have many items you’d like to use on the altar, but not the space to display them all, you can opt to rotate items out. Incorporating offerings of cut flowers, burning incense or candles, and laying out offerings of food and drink are also a great way of connecting with your ancestors via the altar, and in working with them. You don’t need to do this daily, but try to get into the habit of making an offering to them at least weekly.
My uncle when he was alive tended to enjoy a Mr. Goodbar and a Diet Coke daily. So when I want to lay out something special just for him, I’ll put those items on my altar. You can also opt to include a portion of any meal cooked from old family recipes. If you’re like me though and paranoid about bugs, when I lay out food and drink offerings I tell my ancestors to dig in, because in an hour I’m cleaning up.
In my backyard there’s a cutting of a ‘burning bush’ that originally had grown in my Grandmother’s garden. Every year it is the very first item to bloom in the spring weeks before any other plant. During that time I take cuttings of the branches, place them in a vase and lay them out as offerings to my ancestors.
Ultimately so long as you approach your ancestors with respect there’s no wrong or right way to construct an altar, at the end of the day you need to build the altar around things that are meaningful to you as being representative of the ancestors who came before you. As you grow more and more accustomed to working with them, don’t be surprised if you start being inspired or prompted by them to include other items.