Interpreting Art
There are certain recurring images that have been unearthed, which are clues to ancient belief systems:

1) Neolithic megaliths tend to have the following images: spirals, concurrent circles, triangles, zig-zags, possible images of the sun and moon in addition to people.  Look to the Monuments page for illustrations.

2) Iron Age and earlier finds show a preponderance of spoked wheel symbols (representing the sun?).  Other Celtic finds include swastikas, birds, double axes, rosettes, boars and bulls.

3) Certain themes recur when depicting deities: horned gods, triple gods/goddesses, mother goddesses and animism.

4) The stag-god and the bull-horned god (worshipped in Northern areas) are usually not seen with a consort, with a single exception of a single site where he is shown with a horned goddess.That location is the site of Rutupiae.

The basic forms used to decorate megalithic monuments (left to right) dot/cupmark line circle quadrangle arc zigzag wavy line spiral oval
The Power of Three Although this phrase does make people think of a specific TV series, this phrase is extremely appropriate for the Celts as well. Repeatedly in art there are 3's - stellae and statues with 3 heads (tricephalic), the triskele (a three way celtic knot, also can be see on the above referenced show), triple goddesses, etc.
Sun as healer Associating the sun with a healthy glow is an age old concept. The Celts equated the sun god with healing.  Thus solar and wheel images, especially on jewelry, often represent this power.  (Remember: an amulet cannot replace the protective power of a good 48 SPF sunscreen)
Emphatically Torc-ed Torcs (necklace seen to the left) helped to reinforce head worship. They could also be placed on the upper arms ritually extricating, as a torc around the neck does, the top of the body from the rest