I think I mentioned this to you before but I use 1 drop per gallon twice weekly roughly. Now a days I tend to fudge it and just drop in what looks right and adjust it as needed. Some tanks need more nutrients than others do depending on your plants/how heavily stocked you are.
It depends on your bioload of the tank (less bioload usually means more ferts because they don't get as much from fish poo), how many plants you have (more plants means more ferts=more mouths to feed basically).
So start with 1 drop per gallon once a week, if you don't see good growth or your plants getting yellow-ish, go to 1 drop per twice a week and see if that helps. Again, if they're still yellowing go to 2 drops per once a week and 1 drop for the other time (so for example, 2 drops per gal on Saturday and 1 drop per gal on Wednesday), and again last but not least if you still need more; 2 drops per twice a week.
Not all plants draw from the liquid ferts though as I've explained before, some will draw more from their roots (root feeders) like swords and carpet plants (hairgrass, glosso, pygmy chains, etc.) and will need to be supplemented more with root tabs than they will need the liquid ferts.