HEy great news, you all getting your gardens installed.
For your SANDY SOIL, one trick that works wonders is to dig a deep hole, fill it with compost. then cover it with the sand...plant your plant on top of that sand and backfill with a slightly ammended soil blend. (the moisture will stick to the SOIL BLEND buried in the sand....soon the roots will go to the water(they always do) and your sandy soil will support plant life.
For your CLAYEY soils, dont add sand......SAND + CLAY = Concrete.......
Sandy particles are flat and angular (not river sand that is a different topic) but the clay particles adhear to the platey angular sand and they compact.. in 1995 Sunset GARDEN MAGazine came out with a article regarding adding sand to clay soils to improve the texture. IT was retracted later on, Soil Professionals state wide had their hands full trying to reteach folks about this problem.
If you take clay soils and are forced at gun point to add sand....you need to add 70% sand to clay to make it a proper growing medium. Dats alotta Sand.
Clay soils need COMPOST, not just mineralized compost but stable compost,with fiber particles..to hold water and to keep the clay particles from re-touching or recombining. We love it when the garden has 6% organic matter in the soil. Archeologists and researchers belive that the GARDEN OF EDEN soil was 6-10 % organic content. MOst good soils in California are 1% organic matter. You can consult your Ag extension office for tables in your area that will help you determine your soil contents.
bacterilogically alive soils, = compost will fight off disease and other nasty organisms from conquring your garden......if in doubt compost. or stable organic matter........cover crop in turn in and let it over winter and be perpared for a wonderful spring.
best to you, and your gardens,
Jack
Dirtdoctorjak@aol.com
www.Soilstogrow.com
I promise I won't tell, but I won't promise to not play neener neener with our other members. 
