Nails first then tan, the only problem is if someone else is doing the nails the tech must not put moisturisers on the hands afterwards and also not apply the cuticle oil too liberally. ( If I am doing the nails I apply the oils carefully and dont do the mini hand massage with moisturising lotion)The oil wil be a barrier to the tan so I ususally ask my clients to get their nails done a day before the tan or a day after, That way all the creams and oils will be removed before you go to tan them or the tan will fully developed and the nail products shouldn't affect it. Hope this makes sense