Hi
Drift wood from the beach is not a good idea as it will have soaked up salt from the sea which will leach out into your tank, no matter how much you soak it before hand.
I know others on this site have put wood they have found in their gardens or when they were out and about in their tanks and everything has been OK. I beleive you just have to make sure the wood is dead and dry, oh and avoid conifers as some can be toxic to your fish.
I am sure others more experienced than myself will be able to give you additional advice.
Anne