If you're looking for an easy answer, there isn't one. there have been lots of articles, pamphlets, and books written on this subject, but in the end, you'll have to write your own.
So, here's how. Take your rifle to the range, along with patching of various weights/thickness/materials, an adjustable powder measure, pure lead balls calibre specific, and a pencil and notepad. Place your targets at 50 yds/meters...25 will tell you nothing except that you are an exceptional shot! Start with what you consider, using your own intuition, a minimum load, load and shoot five shots into a target YOU CAN SEE WELL, and mark the load on the paper target. Do the same thing again, changing ONLY ONE variable, such as the charge volume, or the ball diameter, or the patch thickness, or the patch lube. Just one. record the results again. Keep this up until you run out of powder, lead or time. Keep these records, and refer to them frequently. It will take you many such trips to the range doing this, changing only one thing at a time, until you have come to the revelation that you have found the best load for that rifle!
Start over with the next rifle.
No one has written the book that will satisfy this journey. The rest of the shooting/loading/data/technique will be found here, on ALR...free.