It's very difficult to create anything that has any significance if you don't properly understand the historical background of the subject you are working in. Celtic Jewelry making is no different, so let's discuss a couple culturally interesting facts about before we get into making something.
Celtic jewelry making has been known to exist since the first century B.C. The Celts strongly believed in reincarnation and so these influences have been incorporated into their jewelry making. Celtic symbolism is all about the immortal as well as the priceless gift to human civilization.
Like:
The Latin Triquetra which literally means the "three cornered" and was later representative of the Holy Trinity.
Man's progress was symbolized by the Greek symbol Triskelion or "three legged". Notice how the knots are like three legs running.
Another interesting thing the Celts did was the concept of the five fold. The fifth fold was an intersection of 4 others. Spring, summer, fall, and winter made up the fifth fold of transitioning.
The infamous Crosses: represents the connection of heaven and earth. This was considered to be our link between the physical and spiritual.
To star, I recommend using copper wire to start bending into knots and interlaced spirals. The Celts excelled in working soft metals into beautiful pieces.
There are literally thousands of ideas you can get from simply searching google for celtic jewelry. Pick a design you would like to try and get started. I recommend you pick stuff that has some kind of personal meaning to you.
Another vital tool is using graph paper to sketch out your patterns.
Celtic jewelry making requires symmetry and if you are not precise enough you aren't going to make anything look decent.
Look for the appropriate wire gauge for your jewelry. If you are making a brooch, choose the chunkier lower gauge ones; and for the bracelet or the ring, select the thinner ones with higher gauge.
Make sure that you cut your wires long enough so you can simply trim off the excess instead of having to throw away expensive wire.
With your left hand, grip the wire using chain nose pliers, then round and curve the wire to your desired pattern. To make smaller loops, use round nose pliers after which, curve the wire using the tip. Bend it further back to make larger loops. Fold the wire, going around the gems and stones to lock into their place. Switch back to the chain nose pliers so you can bend the wires with angles.
Make sure you use clips to secure your creations or they are going to pull apart. At the very least bend the wire into a hook at their ends and use that.