Level up a little bit questing before starting Nashkel mines, e.g. Dreppin's quest (I think that's his name) from the Friendly Arm Inn, clearing out the spiders in Beregost.
If you go east of Beregost you arrive at a Temple, where you can get a really nice quest that nets you a lot of gold and exp - you have to hunt a fallen priest named Bassilus! DSimpson's guide on gamefaqs is really good if you want a guide