To weave a ladder stitch, you will need the following materials:
Beads (either bugle or seed beads)
Beading thread (such as nymo or silamide)
While making ladders, it is important to keep a good hold of your ladder as you progress. This will keep gaps to a minimum. If you still have large gaps after finishing your ladder, and you have used beads with good sized holes (like Japanese beads), then you can thread back through all the rungs. This will help straighten out your ladder a little.