Suggestion 1 :If the jewellery is solid, immerse it in a solution of washing soda - 1 tablespoon of soda to 1 pint (570ml) of hot water. Leave until tarnish has been rmoved, then rinse thoroughly and dry thoroughly.
If the jewellery has any kind of stones, clean with a proprietary silver polish.
Suggestion 2: One of my aunts told me that steeping overnight in gin got all jewellery sparkling, and another told me that steeping in cola did the trick. Mind you, they were as nutty as fruit-cakes, so I can't vouch for either method.