You start by deciding exactly what you want from your yard
Then you take soil samples all over the place to see what you have to work with
Nothing odd to have 5 or more different soil types even on a 1/4 acre block
Then you spend a year taking photos of your yards in the morning , midday & evening so you have a good idea of the sun / shade patterns
In the same dairy record the rainfall and take photos / make records of the run off
Then have a think about your self , back / knee problems , raised beds ?
Once you have all this plot you lot and include overhead / underground services so you don't plant a shrub with invasive root on top of the sewer or drain pipe .
When it comes to finally doing a layout consider sight lines
If you have small children you need reasonably good visuals of the whole yard from the rear of the house
And finally remember there are no strait lines in nature so curves are always the go