An altar an either be a working surface where it is used to store current spells and on the go workings, it can be a shrine to a deity (either specific or general), it can be a secular area of worship where a witch may keep items belonging to her path but with no religious overtones of worship. It can be an area dedicated to nature or the elements or even just a table where magical tools are kept. It can also be a combination of any of the different examples above.
The altar of a Traditional Witch is less likely to be an area for worship than an altar belonging to a Wiccan witch as broadly speaking Trad craft is a secular path and Wicca a religion. However it would be too much of a generalisation to say all Trad altars look one way and all Wiccan altars another. If we were to take a basic overview as to what a witch may (notice may and not must) have on his/her altar it would likely be a selection of items from the list below:
Usually decorative, will likely cover an altar table or in the case of a travelling altar may be set up as the foundation of the altar itself.
Represents the element of water and/or the Goddess and the feminine divine. May be a symbol or may be a practical container for consuming wine or juice during ritual.
The ceremonial knife - used primarily for directing energy and for those witches who do cast circles this is likely to be the tool of choice for doing so. Some witches use this to represent fire on the altar. The wand can be made from wood, crystal, resin (pretty much anything really) and may be used in a similar manner to the athame or more directly used in spell work.
Another symbol both of femininity and also of sexuality. The cauldron is often said to represent the womb from which life will spring. Again a very practical tool for the witch who may use in spell and potion work and may also even cook with it on occasion. Useful for lighting portable fires in as well if you have a cast iron cauldron.
For those making offerings to their Gods of choice offering bowls can be used to hold gifts from nature - cut flowers perhaps or acorns -
A representation of the five elements (the fifth being spirit) - pentacles may be embroidered onto altar cloths, depicted in statuary or formed in designs on the altar with elements from nature. More likely to be found on a Wiccan altar.
Used as a tool for purifying the sacred area and may also be rung at the start and end of ritual to signify the passing from mundane to magical.
Used extensively in spell work and lit to represent fire.
Different incenses will be lit for different purposes. (See pretty much any correspondence table on the internet.) Incense can also be used to represent the element of air.
Used for the different properties inherent in each crystal, to represent earth or to symbolise the different stages of the year.
Symbol of Fire
Candles, fire ashes, even a statue of a dragon could be used.
Symbol of Water
Chalice, bowl of water, shell from the beach.
Symbol of Earth
Tree bark, rocks, crystals, bowl of soil, bowl of salt
Symbol of Air
Incense, feather, statue of a bird, dream catcher
Representation of the God
Statue, gold candle, bottle of sun water. Statue need not necessarily be of the Sun Go. The Green Man may be used, Pan even Baphomet. Depends on your own belief system.
Representation of the Goddess
Statue, silver candle, bottle of moon water. Some statue choices include fairies, mermaids or mythical creatures and then the Virgin Mary has been known to be used.
Fundamentally the choice of what you put on your altar is down to you, it has to mean something to you personally. I tend to change mine with each sabbat to keep it fresh and up to date and each month starts with it looking pristine and ends up a cluttered mess as all the working from the month accumulate on it. My advice to you would be to think about everything on the list and work out what resonates with you personally and what you think you have genuine use for. Use this as a starting point to create your own basis of an altar.
Image - altar belonging to Deguwitchrose