stick to unprocessed foods, just buy fresh veg and fresh meat. if you must have some salt, add it on your plate not when you cook, you'll use far less.
This is really difficult as it's surprising which foods have salt in and how much.I've noticed that if you buy tinned food like baked beans, they usually have a lot salt version as does butter, but it's an absolute nightmare doing a normal shop unless you go with ethandron and just buy fresh food but it's not always that easy to do this.