Move rear sight in the direction you want the bullet groups to move.
If you are hitting left of center, you want your groups to move right, so move rear sight right. Adjustments to the front sight are opposite that logic.
Start at 25 yards.
There are posts here about working up a load. My suggestion is to pick a medium load and work on your ball, lube and patch combo first. There will be so many suggestions that it will make your head spin. When working up a load or changing things, you generally don't adjust your sights until you are done.
As mentioned above, work up a load that will group well first. For example, hold your sight directly on the bull for every shot. Once you find a load that produces groups you like, then you can start adjusting sights to move the group to where you want it to be. Typically you will have the groups print just above the front sight but that's up to you. Then, use that load all the time,knowing that if you change a component or charge weight, your groups may change drastically.