Do your windows look a little bare? Perhaps a crocheted window treatment will help. The free curtain and valance patterns linked below will give you a nice variety of different designs to choose from.
This checkered diamond pattern would make lovely flat curtain panels, if that's how you want to use it. You could also adapt it to make valances as well.
If you already know how to do filet crochet, you can just use the free checkered diamonds chart, and repeat it out as many times as needed to get the right sized curtains. The chart tiles seamlessly.
This pattern works for any size window. The instructions are by Priscilla Hewitt; she has posted them at her website, priscillascrochet.net.
This lacy window treatment features lovely crocheted pineapple motifs.
This filet crochet curtain features a vintage (or possibly vintage-inspired) spring scene of people picking flowers. The free pattern is posted at the Adriafil website.
The link above takes you to a photo of the curtain. If you like it, you can download the pattern plus bunches of random other patterns using the link below; you'll have to scroll down to find the curtain pattern.
It looks like this trim is intended to be attached to a fabric curtain. The free pattern is posted at the Coats Crafts UK website.
This design is by Cindy Adams. The free valance PDF pattern is posted at the Crochet Magazine website.
This lacy curtain features pretty floral designs along the edging. The free pattern was designed by Diane Stone; it is posted at the Crochet World website.