Basic Altar

An altar can be as elaborate as a custom carved church style massive affair with ornate ritual tools placed in specifically measured positions. Or it can be a stump of wood in a forest, a tv tray in your living room, or anything in between.
Most altars change constantly with matron dedication, seasons, sabats, etc.
You can put just about anything you can imagine on your altar, a few common items are;
Candles, incense, a cauldron , salt, a pentagram, a bell, anthame, a statue or representation of the goddess, horned god, or your matron,a wand or broom, and crystals.
I like to use an altar cloth , I always choose a cloth that is pretty, functional, and not too difficult to get wax off of. You know you’re going to be dripping wax from time to time. It’s inevitable. That’s why I use very expensive altar cloths, since I know I can be a messy witch. The altar cloth is generally used to protect the altar, and is not “necessary” but can be meaningful (depending on its symbology) or merely functional.
I try and keep some representation of the elements at all times as well.
Pentacle for North (Earth)
Athame or incense for East (Air)
Wand or candle for South (Fire)
Chalice or Cauldron for West (Water)
Gem stones have different properties, and can be selected to bring healing or draw energies to your altar. You may wish to consciously use color on your altar, to create a specific atmosphere or energy. Every color has its own meaning and power, and using the right one can enhance the overall experience.

Other than that? I like to change seasonally, adding gourds and such in the fall fresh flowers in the spring etc.
You are only limited by your imagination.

I’m not familiar with anyone having Joan of Arc as a matron , I would look at things she was known to enjoy and use trial and error till I felt it was right.