Never tried join-as-you go? Learn all you need to know with (affiliate link) Join As You Go: Seamless Crochet Techniques class from Craftsy. It's taught by a leader in the crochet world too!
Looking for crochet square ideas? Here are two highly recommended suggestions:200 Crochet Blocks by Jan Eaton. It's a beautiful, well organized collection of blocks that plays with both design and colour.
And for amazing vintage Grannies, check out Granny Squares: 20 crochet projects with a vintage vibe by Susan Pinner. Adorable projects and beginner friendly too. This book uses UK crochet terms, just check the end of this post for a handy conversion chart that makes it easy to use no matter your preferred system.
As for my afghan, the granny squares are fairly straightforward, very quick and easy to crochet.
The pattern for the lovely block that made my afghan is called Little Circle Square which can be found on the project page for this afghan on knit and crochet site Ravelry (another great place to find crochet square designs). A quick browse of the dozens of projects folks have crochet from this pattern show the endless possibilities that can be created from this simple design. One of the amazing things about crochet is the creative expression, and one granny square always leads to another. And another.
P.S. Here is a conversion chart with international symbols. Hope it helps!