There are a number of page templates to help get you started.
Each of the templates have a working area of 1024px, H1 starting size and recommendation for body copy width (720px).
Wide - The main content area spans a width of 1024px. Place your content within this area, using the H1 size as a starting point.
Narrow (2 col) - the main content area spans a width of 768px with a right column width of 232px. The right hand column can be turned off if you require a page with a narrow content area only.
Pick the template that is most appropriate for your journey - and stick to the same one throughout.