I would plant some 'backbone' plants - small trees and shrubs - first. Maybe add a boulder or two for interest. Then a fun thing to so is to find a local nursery and buy things every month that are IN BLOOM, which gives you immediate gratification and also builds a diverse garden that looks good every season.. As you learn what you like, and what will grow in your region, you will gradually fill in that lovely area. Everything needs regular watering for a couple years until the roots get established. Depending on your rain pattern, you may need to add irrigation, sprinklers, or soaker hoses. I don't bother with any of that, but I get plenty of rainfall except in late summer. You'll figure that out as things droop (or not).
I do second Debra's suggestion to add bulbs this fall. You will be pleasantly surprised next spring - just be sure to mark them well so you don't dig them up planting other things.
As a newbie, I also suggest opening "My List" as you add plants, as a good tool to keep track of what you have, where it is, and how to take care of it (each entry in "Your List" is also a link to the main database for that particular plant. Check out several member's lists to get an idea of how to organize and categorize.
Pick out a couple forums to 'watch' - your growing region and whatever plants catch your interest. Even if you just lurk, you will learn lots.
Good luck, welcome to NGA, and keep us posted re your progress (we all like to follow projects with photos!).
