I've been using just the all-in-one tablets, but my dishes are no longer getting clean. I read on here that they're no good, so I've bought salt, rinse aid and separate tablets.
So... the tablets are pretty self explanatory. How do I know when it needs rinse aid and salt? Do I put both in every wash, or is it something you leave and top up when it's running low?
How much do I put in and how do I know when they've run out (if it's something you leave) and what should I turn the rinse aid setting thing too - it seems to have some kind of dial? 
Nobody in my family has ever had a dishwasher before and it was second hand from ebay, it didn't come with a manual.