If planting in a raised bed a 4 x 4 or 4 x 8 is a good beginner size. Proportion is the sense that the size of the individual components the landscape plants or groups of components in a landscape is consistent with the landscape as a whole. Southern gardens may benefit from late afternoon shade whereas northern gardens likely need all the sun they can get.
Design from the house outward into the garden.
Watch your dream garden take shape. The mathematical formula for getting a comfy step is 2xheight width 26inches. You need to see how you are going to use your garden before you do anything. Namely proportion transition and unity.
