I don't drink alcohol and there are loads of fish recipes such as Nigella's saki salmon that use alcohol which I really want to try out! What's a good substitution?
In most recipes you can substitute chicken or fish stock (broth) for white wine, in equal quantities. This won't give quite the same depth of flavour but will usually give a good finished dish, particularly if the wine is only in small proportions. In some cases a little wine vinegar can also be used to add flavour, but it is far more acidic than wine itself so quantities need to be reduced and you need a recipe where the acidity can be cooked out.
For the Sake Salmon you could try switching the sake in the marinade for a dash of rice wine vinegar and in the sauce use fish stock instead of sake, but add a teaspoonful of rice wine vinegar. Taste the sauce before adding the fish sauce as you may need to reduce the quantity of fish sauce because you are using fish stock. In risottos (for 4 people quantities) where they may suggest using wine or vermouth, try adding instead a tablespoonful of a good white wine vinegar plus a little stock instead. Let the vinegar cook until the acidic fumes have gone (stand back as it may make your eyes water) then add more stock and cook the risotto as usual. For sweet wines apple or white grape juice can be useful substitutes.