A great resource for designers is a stitch dictionary. If you need some new interesting ideas for your next design but aren't exactly sure what you want to do, a stitch dictionary is a great way to help jumpstart your brain. There are so many types of beautiful stitch patterns to experiment with. Here are a few suggestions. I got these from my local library which is a great place to look for stitch dictionaries and other knitting books.
400 Knitting Stitches: A Complete Dictionary of Essential Stitch Patterns
published by Potter Craft
400 Knitting Stitches is a great resource full of simple and more complex stitch patterns for beginner and advanced designers. The book is divided into eight categories such as "Lacy Stitches" and "Slipped Stitches". Each stitch has a photographic example as well as instructions on how to knit the stitch pattern. There are charts for each stitch pattern as well though they are a little small so you might need a magnifying glass to look at them! The beginning of the book has a helpful knitting basics section for beginners as well.
Up, Down, All-Around Stitch Dictionary
by Wendy Bernard with photographs by Thayer Allyson Gowdy
Up Down, All-Around is a stitch dictionary with over 150 stitch patterns. What is unique about it is that it tells you how to work each stitch pattern in four different ways: top down, bottom up, back and forth, and in the round. I was working on a design and wanted to incorporate a certain stitch. Unfortunately all the instructions I could find online for it were only back and forth, and I wanted to knit it in the round. Thankfully I was able to figure it out for myself, but now that I know about this book I'll definitely be referring to it in future if I run into the same problem with another stitch!
Norah Gaughan's Knitted Cable Sourcebook
by Norah Gaughan with photographs by Jared Flood
I am a big fan of cables myself and love knitting projects with different kinds of cables. If you're like me, you'll definitely want to check out this book that contains 150 cable patterns. There is a section on the basics of cables as well as several patterns using the cables in the books, tips on creating your own cable patterns, and a section on charting. I'll definitely be referring to this beautiful book for future design ideas!