Well, you only need to consider sun exposure while plants are growing. So, before the trees leaf out you can get away with spring flowering bulbs since they won't be shaded.

What I find helpful is to sketch out your property on grid paper (a rough job is fine). At sunrise go mark the grid paper according to sunlight. Full, part or shade. Repeat roughly every couple hours. Add up the hours of each type of sunlight and this gives you a decent idea of the various exposures on your property. Once done it is pretty much set unless you have growing trees.

Find north.....and subsequently east and wast...
You are coming up on the summer solstice, so from now on until the fall equinox, the sun will set more to the south and rise more toward the north.....and then reverse the process.
As the summer progresses one of my perennial beds gets less and less sun due to a big tree that blocks sun on the south west.
Look out and watch at what time the sun hits certain areas and what time they are shaded. Make notes. Any area that gets sun from 10 AM to 3 PM will grow full sun plants very well.
Linda C

Take photos year round at various times of the day....easy! There are many early sun plants that can be put under deciduous trees such as Basket of Gold, Aubretia, Arabis, Candytuft,Anemone, bulbs etc. These perennials either bloom or set their buds in April/May and will give lots of color before the trees leaf out...that's one reason I take pix year round as they love/need winter and early spring sun.