You want hilly or flat? I live in Whittier and ride out near there pretty frequently - my favorite east/west ways of getting from SGRT over to the Yorba Linda area are either Beverly (via turnbull canyon) or Mar Vista over to the Colima area, then janine over to macy and then I'll get on Whittier Blvd all the way to just past Harbor (palm) down to Central/La habra. take that to Birch, which will curve around and turn into Rose and take you straight down to Bastanchary. I usually go west on Bastanchury from that point, but I presume that eastbound will be the same. They've removed bike lanes in parts so that they can add a central turn lane, so that's not cool. you can always divert south to the yorba linda recreational trail if you want to avoid bastanchury, and then just pop up north again on residential streets to get near the HS.
I'm not really sure how to get from Glendale to the SGRT area but I'll whip up a RWGPS route demonstrating what I mean if that's what you're looking for.