Canon 18 55mm Lens
How I can avoid having a history of focus when i shoot canon xsi landscape shots and 18-55mm?

can you tell me what aperture setting I should use? Thank you.

Put the camera in aperture priority mode and set the opening of at least f / 8. I personally use f/22, which is ideal for landscape, which basically gives you all the depth of field can ever want. Although it is difficult to use this mode, if a little nervous about using it for any reason, you can Use Pre-automated mode of the Landscape.