You want to use various keywords and keyword combinations that buyers might use when looking for an item like yours.
You want to repeat the most important keyword frases in both your item title and item tags.
I'll take this set of earrings as an example:
http://www.etsy.com/listing/115034473/lamp-work-chain-link-dangle-earringsYou want to start your item title with the most important keywords (since search engines read from left to right, just like we do).
A possible title might be: 'Dangle earrings, beaded earrings, glass bead earrings'.
Now you want to repeat the same keywords in your tags.
- dangle earrings
- beaded earrings
- glass bead earrings
- lampwork beads
- handmade earrings
- chain link earrings
- beaded jewelry
- glass jewelry
- handmade jewelry
- flower beads
- flower earrings
- glass and silver
- blue and green
- blue green earrings
etc.