Before you start your dishwasher it is essential that you have checked, whether or not the dishwasher lacks salt. Generally dishwashers use a special kind of filter salt, that do not clump. Besides this fact, you also have to adjust your dishwasher to the water hardness in your area. You can get this information by contacting your local water supplier, most of them you can reach by their website, but you can also check the phone book. The formula for converting parts per million (ppm) to degrees Clarke (e) is: 1 ppm equals 0.07e.
If you live in an area where the water is extremely hard (which is over 26 degrees Clarke, 26e, or 370 parts per million of calcium carbonate), it is not necessary that you add extra rinse aid or salt, other than what you get in the all-in-one tablets. Even if the warning light on the dishwasher turns on for lack of salt or rinse aid, you don't have to add anything further. However you can consider if it is necessary to add a little extra rinse aid according to get a squaky clean finish. After all it is advisable, that you use the standard tablets (not the all-in-one) and on your own add salt and rinse aid, if the water hardness in your area is over 26e.
The adding of rinse aid depend on two things; (1) what kind of dishwasher you have and (2) the concentration in the rinse aid you buy. It is important, that your dishwasher does not contain too little or too much rinse aid. Too little rinse aid can cause stains and stripes on your glasses, while too much rinse aid will make your tableware greasy.
Naturally the kind of detergent tablets you use do have a very important function in your dishwasher, because they make your tableware properly clean. However it can be somewhat difficult to make head or tail of what the different kinds of tablets include. The standard tablets only include detergent, while the 2-in-1 tablets both contains detergent and rinse aid. Thereby you only have to add salt on your own, when you buy the 2-in-1 tablets. With the 3-in-1 tablets you get the whole package. These tablets are often very aggressive, and they may cause incrustation on your silverware. So be careful!