When I get lost in planning, I get analytical!
Measure your space and go to a free graph paper generator online so you can get the scale right for you, usually one foot per square (or whatever fits your situation on a single sheet of paper.)
Make a cheat sheet of how much spread to expect on your mature trees and shrubs.
Use scrap graph paper, or even better, a sticky note cut to the size of your future mature tree/shrub. Move your simulated plants around on your graph paper until you're satisfied.
Cardinal directions come into play when figuring for shade. But you should be able to factor that into your projections by studying the site.
And once you're satisfied with your future on paper, stick a few marker flags in the ground you can start digging more secure in the knowledge that you factored in future growth.
Bonus: while your young trees/shrubs are still small and not making much shade yet, you have room between them to sneak in some annual vegetables!
Another tip: download Google Earth Pro on a PC and you will have a tool that shows you past satellite imagery. This has really helped me because you can see different years and different seasons of your site from the comfort of your desk. You can also use Pro to draw and measure superimposed on your site. I will try to do a tutorial on using satellite imagery for garden planning soon.