Mark your borders on cased leather and then cut that border with a swivel knife.
Now use a strait edge and mark a faint line in the damp leather the direction you want your stamping patern to run ( use a blunt tipped object)
You need your basket stamp, and a border tool of some sort.Also a small seeder works well in the corners of the border.
To start the basket stamp just start on the edge of your line at the bottom against your border.
Stamp it into the leather then move the stamp about 3/4 its lenth up the line and stamp again. Continue this till you get to the top of the line.
Now move over and start again at the bottom beside your line of stamp marks. You now line up the ends of your basket stamp to the ends of the stamps you just put in the leather. They should overlap slightly. The secret is to run the stamp as strait as possible and to put the ends your overlaping in the exsisting stamps as cleanly as you can. If your leather is cased properly you should see a nice brown coloring when you pound the stamp in( one or two blows at the most.
When you fill all the area inside your border cuts you can use your border stamp and stamp around the border. When getting close to your border cuts with the basket stamp tip the edge up to keep it from cutting into the leather outside your border.
I stamp on a 3" granite slab and use a special no bounce mallet.
If you need pictures,or more help let me know.